Refund under inverted duty structure - issue with net itc

Sir,

We are one of the manufacturer of pharmaceuticals goods in Pondicherry and we have claimed Refund under Inverted Duty structure for the month of Sep'2018.

Here i have purchased some material in the month of Aug'2017 and filed the return for GSTR-3B on the same month of Aug'2017 but the supplier failed to file return GSTR-1 on Aug'2017 instead they filed on Sep'2018. Now I have taken that ITC for my Sep ‘2018refund claim (We have not taken that ITC for our previous refund claim due to non-filing for GST return by supplier) and shown in the RFD-01A net input tax credit column. But GST officer said that Aug'17 bill ITC is not eligible for Sep'18 refund Claim and need to be disallow from RFD-01A net ITC. if I said to officer , When supplier file the GSTR-1 , then only it will reflect on GSTR-2A and eligible for Refund claim but they are not accept and asking the notification for that .

Kindly suggest us for the above claim process.

Thanks and Regards,

P.Pushparaj,

Pondicherry .