(a) A retail installment contract may provide that if an installment remains unpaid after the 10th day after the maturity of the installment the retail seller may collect:
(1) a delinquency charge that is not more than five percent of an installment or $5, whichever is less; or
(2) interest on the amount of the installment accruing after the maturity of the installment at a rate that does not exceed the maximum rate authorized for the contract.
(b) Only one delinquency charge may be collected under Subsection (a) on an installment regardless of the duration of the default.