Whenever a retailer has collected a sales tax from a customer in excess of the amount prescribed or due under this chapter, and if the retailer does not refund the excessive tax collected to the customer, the amount so collected by the retailer must be paid by the retailer to the tax commissioner in the return filed for the period in which the excessive collection occurred. If the excessive collection is subsequently refunded by the retailer to the customer, the retailer may file an amended return with the tax commissioner for the period the excess tax was collected and file a claim for refund.