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. Florida law requires that refund applications be supported with sufficient information and documentation to determine eligibility and the refund amount due. I have overpayment on unemployment. The demand letter will explain why you got overpaid, how much you need to pay back and the deadline for submitting it.