Hi there, it is an unusual situation that you are in but, as it happens, but one that I have successfully managed. I became a Canadian PR in 2005 but unfortunately got a conviction in the UK in 2010 and returned to Canada in 2016 after my conviction was spent. Most of the advice on this forum and elsewhere typically related to "foreign nationals" trying to enter Canada. The situation for Permanent Residents of Canada is VERY different... it took me 18 months to become an expert in this, so happy to share my experience.

Firstly, some questions:

1) when did you become a PR and how many years are left on your PR card?
2) are you out of the "sponsorship period" assuming that you obtained PR through being sponsored by a Canadian national? 
3) How much time have you spent in total inside Canada or outside Canada together with your Canadian husband since you first became a landed immigrant? As you know, you need 730 days out of every five years to retain Canadian PR status?
4) When you said "My husband and I went to Canadian Embassy and they could not help." what did you tell them, and did you give them your PR card ID or passport? Who did you meet and how did you get the appointment?

The good news: if you have valid PR status and a current PR card that has not expired, you are allowed to board a plane to Canada. Also, on arriving in Canada, it is not necessarily the case that you will be pulled aside by the CBSA and asked about the conviction. It is not necessarily the case they will proactively know about it. Also, even if they do ask you about it, the cannot stop you entering Canada. There is no decision made at the airport to deny a Permanent Resident entry to Canada on the grounds of a foreign conviction. It has to be assessed at a subsequent interview and potentially what is called an Immigration Division hearing. This will take some time. In the mean time you are free to come and go into and out of Canada. 

Also, the good news is that you are likely not to be found inadmissible to Canada should you wait sufficient time for the convictions to be spent which in your case would be 4 years on top of 22 months. But that is a long time to wait. Also, you cannot simply sit outside Canada for that period, as you will fail to meet the Residency Obligation of 2 years out of 5 *unless* your Canadian husband is living with you for some time in the UK. This counts as "time in Canada" as far as the Residency Obligation for Canadian Permanent residents is concerned. In theory, you could maintain PR status simply by ensuring your husband is with you for at least 2 years out of 5 until such time as your conviction is "spent" in the UK, after which you are unlikely to be found inadmissible on your return to Canada based on the Burgon ruling which was to do with a British person who had a spent conviction who was therefore deemed not to be inadmissible to Canada. This document is worth printing and reading that mentions the case law: https://www.irb-cisr.gc.ca/Eng/BoaCom/references/LegJur/Documents/RoaAmr08_e.pdf

After you have completed the 300 hours community service, you could wait until the last possible moment to return to Canada, say a month before your current PR card expires, and then return to Canada for good. By that time you will almost have spent status. The interesting thing for PRs is that a PR cannot be found inadmissible to Canada for minor crimes and so they go through a process of finding the equivalent of what the UK conviction is in Canada and looking at the maximum sentence that *could* have been imposed had your actions been conducted in Canada. If the maximum sentence could have been 10 years or more in Canada that counts as "Serious Criminality" and would potentially make you inadmissible after a review. However, if your conviction is spent and by the time an Admissibility Hearing comes your conviction is spent there is a powerful case for your conviction being considered equivalent to a Canadian Record Suspension.

Some thoughts & suggestions:

a) Read up on IRPA section 36 available here very carefully: https://laws.justice.gc.ca/eng/acts/i-2.5/page-8.html#h-23
b) Find the equivalent offence in Canada that has the "essential ingredients" of the offence in the UK and look to see what the maximum sentence would have been in Canada. It is highly likely it is 10 years or more, which would put you in the "Serious Criminality" case which would mean that the Canadian IRCC could request a hearing to request removal of your status. However, the process could take a year or more to happen depending on where your "home address" is in Canada (different IRCC offices have different backlogs of cases)
c) Do *not* hire an immigration consultant, as the one I used that has advertised on the internet was not helpful. You *must" have an immigration lawyer from an immigration law firm NOT a consultant (I can advise on this as I have personally had success, but I am not sure how I can share this info with you). A lawyer should be able to help you on a fixed fee basis. In any case it may be a little early to hire one, but by all means your husband could go and see one and discuss it.
d) Do NOT apply to the Canadian High Commission in London or notify them or apply for Criminal Rehabilitation. You are NOT a Foreign National as far as Canada is concerned and so you do NOT need an ETA to fly to Canada. Only a valid PR card is needed. And that is all the airline will ask to see. You do not need to tell the airline about the conviction. You may not be able to do online check-in as they will want to see your valid PR card. I had this problem when  went to Canada in January, I could not do online check-in, but they looked at my PR card at the airport, called Canada to check my status and they had to let me on board. I have NEVER been asked any questions about my conviction by Canadian CBSA on entry to Canada on the two times I entered Canada since my conviction.
e) You have stronger appeals by dealing with the criminal conviction INSIDE Canada by applying for Criminal Rehabilitation after your conviction is spent. I must re-iterate, DO NOT apply or inform the Canadian High Commission in London. By law, you do NOT need to inform the High Commission in London of your conviction nor do you need to apply for Criminal Rehabilitation outside Canada. All PRs of Canada have legal right of entry to Canada as long as they have a valid PR card that has not expired. As far as travel is concerned PRs do NOT need an ETA to board a plane. PRs are NOT in fact allowed to apply for an ETA. Just a valid PR card.
f) You must deal with the conviction from inside Canada, not outside as there are much stronger appeals and a better chances to get the result you want dealing with the matter inside Canada. You can potentially drag out the time it takes to the hearing to make sure that by the time of the hearing your conviction is spent.
g) Try to arrange such that your husband spends sufficient time with you in the UK so that you can satisfy the 2 years our of 5 years Residency Obligation. As a reminder, any time your husband spends time with you in the UK and is living with you, counts as if you are actually in Canada as far as the Residency Obligation for PRs is concerned
h) Ensure that you return to Canada BEFORE your PR card expires, but as close to the date at which your conviction is spent. Otherwise you will not be able to board a plane back to Canada and have to apply for a PR card renewal outside Canada which creates a risk as they could be alerted to the conviction then, even though the renewal form asks no questions on this.
i) When I entered Canada for the first time after my conviction, the CBSA did not ask me a SINGLE QUESTION about my conviction despite having me waiting for two hours. There is a significant chance that you will not be questioned unless you personally raise it (which you do not need to). Also, as far as I know, you have no legal requirement to answer any questions and the CBSA MUST allow a Permanent Resident to enter Canada by law.  But you must answer truthfully. You cannot lie to any officer as they record all the conversations and take transcripts and any lie can bar you from Canada for a very long time!!! CBSA cannot stop you entering but they can report you to immigration if they have any suspicions of criminality in which Immigration will arrange for an interview and may schedule an Admissibility Hearing in the months/years afterwards for which you will have ample time to prepare. The burden of proof (that you are criminally inadmissible) at an Admissibility Hearing lies with Canadian immigration NOT you because of your rights as a PR! Foreign Nationals do not have this privilege.
j) In the best case scenario, you wait a year or two in the UK, keep your head down, then take a flight to Canada when you are ready to leave everything behind in the UK and then stay in Canada for good. There is no automatic tracking of PRs with criminal databases, so you could well enter Canada and, as long as you stay in Canada and don't risk re-entry you could in theory sit out in Canada while waiting for your conviction to be spent. Also, when it comes to renewal of the PR card, there is no check box or question to ask if you have a criminal conviction. After your conviction is spent you can apply for Criminal Rehabilitation (formal acceptance by Canada that you are not inadmissible) inside Canada by application form with the help of the lawyer *after* you receive spent status.
k) For Citizenship, you are likely to be able to obtain it provided the conviction is spent, and as long as it has been at least four years since the conviction as per: https://www.cic.gc.ca/english/citizenship/situations.asp

Overall, your situation is not the end of the world, in respect of being able to return to live and stay in Canada, because you are a current PR. However, you could be stripped of the status at an Admissibility Hearing if you return TOO EARLY and are not (by the time of any hearing) in possession of a spent status which is usually good enough to remove any criminal inadmissibility unless the crime was very serious indeed such as murder. As the amount of money involved in your case was not huge, I do not think you will have a problem, but the lawyer can confirm all this. There is currently a private members bill that I think is aiming to shorten the rehabilitation periods downwards, but it seems it may have difficulty getting through the House of Commons.

On balance I would say get your sentence completed in terms of the community service etc. Have your husband over for a few months this year. Read up along the lines I have summarized. Plan to return to Canada some time before your PR card expires. And DO NOT inform or request permission or apply for Criminal Rehabilitation to the High Commission in London as you are far better off dealing with it inside Canada than in the UK as you have more legal options and the process will be slower. Any review in the UK High Commission will be on the basis of your conviction now *without* spent status and that could likely mean a loss of PR status, whereas waiting some time in the UK and then running the gauntlet at the airport with only a year or two before your conviction is spent means you have a better chance of being able to retain PR status and then become a citizen after that.

I am not sure if private messages are allowed on this forum but if so, I may be able to point you in the direction of the very good law firm that helped me with my case. There are some good and bad law firms out there, but best to retain one before you are planning to return so you can be prepared in case you are asked about it at the airport.

I may be slow in replying but I will get back to you if you have any questions!