Where a dealer, in the case of an assessment completed under sub-section (4) of section 8 satisfies the Commissioner, within one month from the date of service of a notice of demand as hereinafter provided, that he was prevented by sufficient cause from making the return required by section 7 or that he had not been served with the notice under sub-section (2) of section 8 or that he had not had a reasonable opportunity to comply, or was prevented by sufficient cause from complying with the terms of the notice, the Commissioner shall cancel the assessment and make a fresh assessment in accordance with the provisions of section 8.