On the first day, I changed a 100 at the bank counter, and called me the next day to say that there was something wrong with the money.

Ignore the bank, unless the bank comes up with evidence to prove that the hundred dollars are yours. Because now the bank has changed it for you, and the money has been recognized as real money. I'll call you later, unless the bank can prove that the money is yours, it's meaningless to be reasonable. Don't banks have their own slogans? Cash is counted face to face, not responsible for leaving the cabinet. If the bank produces evidence to prove that the money is yours, if you feel guilty, you can change it at the bank. If you are afraid of trouble, let them come to your house. If you don't want to give it, you can ignore him. In general, banks can't prove it. Even if they can prove it, it's useless if you don't approve it.