If any employing unit which has failed to make reports as required under Chapters 27 through 41 of this Title or has filed incorrect or insufficient reports and has been notified by the Commission of its failure and refuses or neglects within fifteen days after such notice has been mailed to it to file a proper report, the Commission shall determine the amount of the wages payable for employment by such employing unit for the period for which the report is required according to its best information and belief and shall thereupon determine the amount of contribution due, if any, computing it at double the rate which would otherwise apply. The Commission in such a case may allow further time, not to exceed fifteen days, for the filing of the report.