If my bank accidentally paid off my entire credit card balance when I instructed them to pay the minimum payment, I'd be glad that it's between the bank and the credit card company. Not sure if I have an agreement with my bank to repay them, and under what terms.
This reminds me of a story. A friend of mine once had a significant amount of money (several thousand euro) deposited into his account accidentally. Being a bit of a shyster he left it alone for several months but eventually started spending it.
Some years later he got several phone calls from his bank all in a very short period of time. His luck ran out. Apparently what had happened is that he'd been in the bank having something changed on his account, the next person came in to deposit money but the teller failed to change the account.
In the end they arranged a very low interest loan for him to pay back the money over time, so in the end he probably came out ahead.
