You wouldn't want the bank to undo the transaction just to then be responsible for giving a paper check to the HOA for the same amount minus $3.50 or whatever. Or at least I wouldn't. The best course of action here is for OP to be more clear about exactly what they're seeing (screenshot and URL) and to demand the HOA refund the overpayment. HOA will comply if OP is showing them evidence and indicating they're willing to go to court for it with that same evidence. OP would win in court but only if they actually follow through and sue soon after HOA refuses. Not suing and continuing to use the service anyway could indicate to the judge that they understood the actual fee to be whatever was actually being charged rather than what the website says. Personally I wouldn't bother suing over $3.50 but that's up to OP.