Credit to owner on prepayment.

Any buyer may pay in full at any time before maturity the debt of any home improvement contract and in so paying such debt shall receive a refund credit thereon for such anticipation of payments. The amount of such refund shall represent at least as great a proportion of the time price differential charge or other interest charge, after first deducting from such charge an acquisition cost of $25, as the sum of the monthly time balances after the month in which prepayment is made, bears to the sum of all the monthly time balances under the schedule of payments in the home improvement contract. When the amount of credit is less than $1 no refund need be made.