IMPORT BY POST

I HAVE A QUERY REGARDING IMPORT

I HAVE A CLIENT WHO IS IMPORTING BY POST.

BUT CUSTOM OFFICER IN POST OFFICE DOESN'T CHARGE CUSTOMS DUTIES AND IGST

I SAID TO HIM THAT HE SHOULD SAY THEM TO CHARGE CUSTOMS AND IGST BUT CUSTOM DEPARTMENT IS SAYING THAT WE WILL CHARGE IT BUT NO GUARANTEE THAT WE WILL FILE ANY RETURN AND CREDIT WILL BE AVAILABLE TO YOU

MY QUESTION IS HOW TO FILE RETURN IN THIS CASE.