they love this kind of problem

I once accidentally found out an error in their netbanking system in Brazil that enabled customers to get a credit "refund" for a scheduled debit of the same amount that hadn't occurred. the imbalance was adjusted at close of day, but the credit remained available throughout a whole day. the maximum amount per such transaction was BRL 10G (some USD 3G back then), but multiple such transactions could be scheduled for the same day, so it was virtually unlimited.

now here's the kicker: I reported it as soon as I found out about it, and assumed they'd fix it right away. but it remained unfixed for over half a year, when I accidentally hit it again. then I reported it again, going for the limit of a single transaction. they called me very early in the morning the next day, reassured me that they'd fix it right away, and sought reassurance that I wasn't going to run away with the balance.

I didn't even get a lousy T-shirt, and then they sold their operations in Brazil to a bank that has been enshittifying service to no end, to the point of having lost court cases about it, and choosing to not comply with the court order to restore the service. I almost long for Citibank's service. then I realize they'd probably have gone down the same paths, possibly even faster.