Gst tax payment in cgst sgst instead of igst, problem in gstr 9 17-18

Hi all,

I have a query regarding GSTR 9.

I Provided the inter-state services in Dec 2017. But my mistake update in CGST and SGST in both 3B and GSTR 1.

Other Party claimed it as IGST.

Now while filing GSTR9 other party is saying that they claimed IGST in Dec. 17 so in 2017-18 GSTR9 there is deficiency of this tax amount. and saying its your mistake so you need to pay this tax amount otherwise I will deduct from your payments.

Please suggest what I can do and what i can suggest to other party to do. Because tax was already paid. And this service receiver is one of the main client.

Please suggest.

Or call me Ravi - 8368504879.