Under Reg E, can a customer dispute an NSF fee for an "unauthorized" ACH debit that did not post to the account?

After making an inquiry with the bank, the customer was provided details for the NSF fee but further charged that the ACH debit was not authorized. The ACH debit was returned, but because of the customer's claim, must the bank reimburse the NSF fee and proceed with an investigation?

Looking for some good advice.

A

205.11(c) Comment:

6. Correction of an error. If the financial institution determines an error occurred, within either the 10-day or 45-day period, it must correct the error (subject to the liability provisions of §§205.6 (a) and (b)) including, where applicable, the crediting of interest and the refunding of any fees imposed by the institution.

If the original ACH debit was unauthorized, you must refund the fee regardless of whether you previously returned the item.