cancellation of gst no.

sir
a firm was registered under gst.act.
in the month of December 2019 and cancelled so moto on 22 Feb. 2019.
there was some sale and purchase during the periods and gstr 1 and 3b were filled.
now which returns are to be filled
or what process should I follow
please guide me.
I have got a notice u/s 46 for the tax period of March 2019
now what to do

thanks