Dear Mam,
As per the provisions of GST Act, GST registration can be cancelled only after filing the GST returns up to the date of cancellation of registration. And filing return form May 2018 till October 2020 will cost you a very huge penalty and late filing fees.
I suggest you to please apply for the cancellation online on www.gst.gov.in and after receiving any communication from the department you may clearly explain the situation to the concerned office and request them for Suo Moto cancelation.
Thanks and Regards
Divya Chugh