A customer claims that they were charged a fee for a service they never requested or used. How should the bank handle the complaint and ensure customer satisfaction?

I. The bank should thoroughly review the customer's account details, transaction history, and statements to invalidate the claim made by the customer and to prove that the customer had indeed stated a preference against the service in question.

II. If it is determined that an unauthorized fee was incorrectly charged, the bank should promptly apologize to the customer, explain the error, and initiate a refund for the amount deducted.

III. Assess and review internal procedures to identify the root cause of the issue, ensuring that similar errors are not repeated in the future by implementing necessary changes and establishing robust checks and balances within the system.