Appeal for Reopen of gst registation

You shall apply for revocation of Cancellation of GST registration

Timing for revocation has expired

You can't appeal on any ground in that case 

You need to apply for new registration.

Why department has cancelled the number ????? & why you did not file revocation on time ??

The client didn't finish their returns and at the time of cancellation client didn't respond for reopen gst and now it was saying please reopen my gst

Within 30 days of cancellation -You can file a revocation application...

If you have the valid reason to proof that return was not filed due to some genuine problems & the same has been informed via mail to department , then the appeal can be filed.
Else need to apply for new Registration.

Yes in case the reference of Section 63 of CGST comes here the safe taxpayer whose registration has been cancelled.
the said section states that if a person was liable to pay tax after cancellation of registration,the proper officer may proceed to assess the liability of said unregistered person to best judgement assessment & issue assessment order.

Note : Cannot obtain Registration on same PAN on which the registration has been cancelled due to non filing of return . (Reference Circular 95/4/2019)