How to File a Refund Claim. Below are the ways you can submit a repayment.This brief but important letter notifies a customer that he or she has overpaid you. It can serve as a very good customer relations letter. You have to tell your credit or debit card company about any error you're disputing within 60 days of when the first statement with the charge was sent to you. Our document template is designed to make the process of writing an "Inform a Customer of an Overpayment" letter quick, easy, and stress-free. The salary overpayment resulted because .