An overpayment may also be generated if you are entitled to a refundable credit that exceeds the amount of tax due. If the DUA says that you were overpaid, you can challenge their decision.You can also challenge the amount of the overpayment. Credit or Refund. 1. Only applies if Overpayment is greater than zero - Enter "C" for. A refund check is issued to a taxpayer who has a credit balance on their bill, provided that they supply the Tax Collector with the proper information.