Cancellation of GST registration

I have migrated from Service tax to GST on 1july 2017 and submitted all the docs for registration thinking that migration was mandatory. I have been allotted GSTIN no. Since my income from business is far below the GST exemption limit I have applied for cancellation of the provisional registration allotted to me on 27. 10.2017 by submitting Form REG 29 online( date on which the cancellation option was made available on the portal). Immediately I got a mail confirming cancellation of GST provisional registration, subject to verification by jurisdictional authority. Subsequently my GST profile was also disabled by the system. Since I have not issued any invoices during period till cancellation application I have not submitted GST returns. Now I have been asked to submit returns till Feb 2018. kindly clarify the legal position / procedure s to be followed.
Anticipating an early reply
Dileep