When an entity that is authorized by the laws of this state to make loans or grant extensions of credit is paid by check to retire all or a part of a loan or extension of credit, and such check is returned because of insufficient funds, and the lender is charged a fee or service charge as a result of such return, the lender shall be authorized to add the actual amount of such fee or service charge up to a maximum amount of Fifteen Dollars ($15.00) to the principal of the unpaid balance of the loan or extension of credit.