ITC REVERSAL NOTICE FROM DEPARTMENT

Hi sir,
my clint was filed 207-18, and 2018-19, filled G-1 , G-3B, after due date. FILLING DATE IS AUG- 2020. TWO FINANCIAL YEARS FILLED.
SO NOW DEPARTMENT WAS ISSUE NOTICE REVERSE THE ALL ITC WITH INTREST. SO HOW TO SLOVE THIS ISSUE
SIR.