Gst after surrendrer of gst

Hai

A person while verifying his bank statements came to know that few of his clients paid GST amount on his service along with the service fees but he surrendered his GSTN(Turnover less than 20 lakh).Now GSTN was cancelled by DEPT.Even he didn't rise any invoice also.So, now is their any way to pay or How he can overcome the problem?(Please suggest  all the possible ways)

*PLEASE IT'S VERY URGENT