FORM GSTR – 3A Return Defaulter notice.

I file GST returns on a quarterly basis.  I have filed GSTR1 and 3B for April-Jun 2021 and Jul-Sep 2021 already.

But I have received notice for not filing GSTR3B for October and asked to furnish tax liability within 15 days.

GSTR-3B for Oct-Dec can only be filed during Jan-22 since I file on a quarterly basis.

How do I respond to this email?

Thanks for the help,

Gnana