If the City Clerk upon investigation or upon checking returns finds that the fee on tax paid is more than the amount required of the taxpayer, he shall, upon request of the taxpayer, refund the amount overpaid by warrant upon the General Fund, or credit the amount against any tax due or to become due from such taxpayer hereunder. If the City Clerk finds that the fee or tax paid is less than required, he shall send a statement to the taxpayer showing the balance due, who shall within 10 days of the receipt of the statement pay the amount shown thereon.