Notwithstanding the provisions of any premium finance agreement to the contrary, any insured may pay the obligation in full at any time before maturity of the final installment. If he does so, he shall receive a refund credit of the unearned finance charge computed in accordance with Section 18635 or 18637, except where the amount of the refund credit is less than one dollar ($1) no refund need be made, and except that where the earned finance charge amounts to less than the minimum finance charge permitted by Section 18627, the company may retain as an earned finance charge a sum equal to the minimum permitted by Section 18627 or the maximum prescribed by Section 18627,
whichever is applicable.