(1) Refunds due to overpayment of fees may be requested at any time within five years from the due date of the return to which the overpayment applies. Refunds may be requested by filing an amended return for the quarter in which the fee was overpaid together with a narrative explanation of the cause of the overpayment. The department shall refund the amount of the excess payment with interest. Interest shall be calculated on the excess amount at the rate of 0.5% a month or a fraction of a month from the date of the excess payment until the date of the refund.