CANCELLATION OF GST NUMBER

Yes you have to file Final Return.

Yes as per Section 45 required to file GSTR 10 within three months from date of order of cancellation. (Not in case of composition dealer)
And also required to Furnish annual return for Fy 2019-20 subject to conditions prescribed in Notification 47/2019 CT (Optional for taxpayer whose Turnover is below 2crore)

Sir me adopted for composite scheme... till I have not received any cancellation order from tax officer.....whats should I do if I received cancellation order