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.The salary overpayment resulted because . If we have identified an overpayment and request a refund, please mail the check along with a copy of the overpayment request letter we sent you. 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.