D.C. Mun. Regs. tit. 16, r. 16-327
If insurance for which a charge is included in a retail installment contract is canceled or the premium adjusted, any refund of the insurance premium received by the holder shall be credited to installments of the instrument of security maturing thereafter.
Except to the extent that the refund is applied toward payment for similar insurance protecting the interests of the buyer and the holder, or either of them, it shall be applied to the earliest installment of the contract maturing thereafter; or at the option of the holder, the refund (plus interest thereon at the rate of eight percent (8%) per annum from the date on which the refund becomes available to the date it is applied to the indebtedness of the purchaser) may be applied to installments maturing subsequent to the earliest installments.
D.C. Mun. Regs. tit. 16, r. 16-327