(1) If the time for the payment of any part of a deficiency is extended, the commission shall collect as a part of the tax interest on the part of the deficiency (the time for payment of which is so extended) at the rate prescribed in Section 59-1-402 for the period of the extension, and shall collect no other interest on such part of the deficiency for such period.

(2) If the part of the deficiency (the time for payment of which is so extended) is not paid in accordance with the terms of the extension, the commission shall collect as a part of the tax interest on such unpaid amount at the rate prescribed in Section 59-1-402 for the period from the time fixed by the terms of the extension for its payment until it is paid, and shall collect no other interest on such unpaid amount for such period.