Employment security administrative contingency assessments must accrue and become payable by each employer who is subject to the assessments as defined in Section 41-27-410 for each calendar year in which he is subject to Chapters 27 through 41 of this title with respect to wages for employment. The assessments are due and payable by each subject employer to the commission for the employment security administrative contingency fund and are not deductible, in whole or in part, from the wages of individuals in the employer's employ. No determination and assessments may be instituted more than four years after the last day of the month immediately following the calendar quarter for which the assessments were payable. This proviso does not apply to any employer if the commission finds that the employer wilfully failed to report when required to do so by the provisions of this section or the rules of the commission, or has knowingly made a false statement or has intentionally failed to disclose a material fact.