late filing fees issue

Today I have nil return of gstr 3b filed for the month of October
To Feb. Before return filing of respective month it first asked for payment of late fees, then go on.
I did that means paid the amount whatever portal asking and having successfully filed, also cleared all the late fees of respective month
Now I have filed nil return of gstr 3b for the march month, it asking 280 late fee payment,
But mar due date is 20th Apr 2018, but why it asked for payment of mar gstr 3b

Please clear this issue