Section 13. A. Notwithstanding the provisions of any retail installment sale agreement to the contrary, a buyer may pay it in full at any time before the maturity of the final installment thereof, and, if he does so, shall receive and be entitled to receive a refund credit thereon and, if the retail installment sale agreement included an amount for insurance, a further refund credit thereon for such anticipation, whether or not the maturity of the scheduled payment of the agreement was accelerated by the holder by reason of a buyer's default.

B. Except as provided in subsection C, a refund credit shall be computed on a method which is at least as favorable to the buyer as the actuarial method, so-called. If the prepayment is made other than on an installment due date it shall be deemed to have been made on the first installment due date if the prepayment is before that date, and in any other case it shall be deemed to have been made on the next preceding or next succeeding installment due date, whichever is nearer to the date of prepayment. In the event a contract has been extended and is prepaid in full during an extension period the buyer shall receive, in addition, the refund of that portion of the extension charge applicable to any unexpired months of the extension period.

C. Where the amount of credit for anticipation of payment is less than one dollar, no refund need be made.

D. On contracts payable in substantially equal successive monthly installments, commencing two or more months after the date of the contract, the computational period for refund shall commence with the date of the contract or, if the goods are delivered or services performed ten days or more after the date of the contract, the computational period shall commence with the date of delivery or performance of the services.