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.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. An overpayment may occur when a claimant is paid unemployment insurance benefits and is later found to not be eligible for those benefits. The documents must show that you paid the taxes for the Tax Year and Installment when the overpayment occurred. Taxes are due in the year after they are passed. The salary overpayment resulted because . The IRS uses Letter 3286C to inform you that they believe you may have overpaid for a particular year and will refund you the difference. In this article, we'll provide tips on how to handle refund request letters and 7 sample templates you can use to get started today!