Researching prior statements for the UT in question would prevent situations like this from occurring. Going forward I recommend researching prior statements to verify the bank was notified within the appropriate time frames (within 60 days of when the UT first transmitted on a statement) and to determine if the UT was preventable (if the bank had been aware), both of which will affect the amount of the customer’s liability.
From the information you provided, it sounds like you weren’t technically liable for the claim you already paid, but if you revoke it now you are out of your timeframes for handling the dispute, so if you reopen it, you may create more headaches for yourself later on.