Voluntary GST registration cancellation

as per notification 10/2017 Intrigated Tax on dt. 13-10-17, I applying GST cancellation on GST portal but options not available. on Dt. 12-01-18 option available then I was applied GST cancel.
between these period I file NIL returns. because my income less than 20 lakh.
but department says you file tax, why I fill tax between these period option not available it not my mistake.
kindly guide me how Can solve it.