How to remove hidden files from macOS and iPhone?

That is just the go to response from your bank and there is nothing on your devices that needs changing. If you say you did not give out your account details, the next thing they will say is that it must be your device. Your financial account details were exposed and that likely was due to one of the thousands of phishing messages, many of which have been posted here for verification. The most common ones claim they are from Apple saying a charge occurred and provide a phone number/link. It is not Apple and you are making contact with the scammer and giving them your financial details. There are no hidden files on your Mac or iPhone that caused the problem.

I suspect this may have happened more than once. Use messages/emails as information only and never call a number or click a link. You always have the option to use known information to verify without one provided in that message/email.

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

You have not been "hacked".

Tell your bank you've done that. It's faster than arguing.