Cancellation of GST Registration Number...

Dear Experts

We are closing down our business in the Month of April 2018. We have filed GSTR 1 (Outward Supplies) till March 2018. 
But haven't filed GSTR 3B since December ( pending 4 months - Dec, Jan, Feb, March).
So my question is can we proceed to cancel our registration now or first we have to file all the requisite returns and then cancel. 
Moreover, the returns submitted till now is NILL ( Both for GSTR 1 and GSTR 3B as well ).

Thank You in Advance...