CANCELLATION OF GST REGISTRATION

If the proper officer is satisfied he can revoke the cancellation of registration by an order in FORM GST REG-22 within 30 days from the date of receipt of the application. Reasons for revocation of cancellation of registration must be recorded in writing.

Please look into the notice again, the department must have asked for filing of GST Registration, All pending returns upto the date of  application for cancellation have to be filed.