The Medical claim was paid after policy was cancelled insurance wants repayment from customer?

DO NOT SEND THE MONEY BACK!!! It was THEIR mistake! They "train" claim processors to assess and pay their claims, which is one of the insurance company's excuses for such high premiums (strange, but true)....if they paid the claim AFTER the insurance policy was cancelled, it only reflects poor training on the insurance company's end...OK, human error, but how is it YOUR fault? And believe you me, if you were in "error" of missing a monthly premium or not paying it in full for whatever reason, there would be no room on their end for YOUR error. I deal w/ ins. co's every day (I work for a surgeon) and you are not legally obligated to return that money!