How to find out if this is insurance fraud...?

Well, they can do anything with that check that they want to. YOU are not party to any insurance claim. You will have to sue them directly to get the boarding money. Or sell the dog, or put it down - whatever it is you normally do, when someone abandons their animal to you. Which is what sounds like what happened.

As it is several weeks, and you have had no contact with the dog's owners, I think you can assume the matter has probably slipped their minds.

One possibility would be to go the where they live and see if they are still there or if neighbours know where they might have gone.

It might also be worth sending that fax as you suggest, because the insurance company, if it exists will be interested.

I wouldn't totally panic yet. If this was a large enough fire to have them relocated out of the house, it could take months to get back into the place. If this is the case, I'm sure that they are very busy trying to get their lives back in order.

Or they could have dumped the dog on you. Either way, you are not a party to the claim, so the company will not pay you. They might, however, be interested in knowing that they paid a bill for loss of use that was not incurred.

I would try faxing the letter, it doesnt hurt to try.

you're stuck will the dog, if you don't know where they are, you cant carry them to court, chances are they moved out of the district they did live in, sorry.