If any taxpayer fails, neglects or refuses to make his return as and when required hereunder, the finance director is authorized and directed to determine the amount of tax payable and by mail to notify such taxpayer of the amount so determined. The amount so fixed shall thereupon become the tax and be immediately due and payable unless the taxpayer shall file a true and correct return with full payment within seven days of the date such mail notification is sent. (Ord. 2546 § 2 (part), 2010: Ord. 505 § 14, 1969).