CAN GST BE CANCELLED FROM BACK DATE IF RETURNS FILED UPTODATE

A proprietorship firm was converted into partnership w.e.f.  19/05/2019. However, GST registration was taken voluntarily in F.Y. 2020-21 as turnover was below taxable in 2019-20. The proprietorship firm has been filing NIL GST return after 19/05/2019 and has filed the same till 31/03/2021. Now, the firm wishes to surrender registration. Whether the registration should be cancelled from 19/05/2019 or from current date and what should be the reason for cancellation.