Input tax credit - Goods and Services Tax - GST

Dear experts, My case is that a CA of the client had inadvertently shown more tax payable in GSTR-3B as compared to GSTR-1 by Rs 18,00,000. This is evident by the report at the gst website. Ideally the that CA should adjust the amount in the sales column. However, in order to rectify the amount he showed the same as input tax credit in the third month. Now there is a difference of rs 18 lakhs in GSTR-2A and GSTR-3B since such amount will not appear in GSTR-2A . It is clearly a rectification of outward liability and not input tax credit taken. The department is demanding reversal of input tax credit along with interest. Is it a good case to argue? Are there any case laws to refer?