Cencellation of assessment.

Where a dealer, in the case of an assessment completed under sub-section (4) of section 9, satisfies the Commissioner, within one month from the date of issue of a notice of demand as hereinafter provided, that he was prevented by sufficient cause from making the return required by section 8 or that he did not receive the notice issued under sub-section (2) of section 8, sub-section (2) of section 9, or that he had not a reasonable opportunity to