GSTR-1 & GSTR 3-B Mismatch

VIKRAM SHAHI (Accountant) (46 Points)

23 July 2018  
We opted for qtrly return last year. July GSTR-1 was filed on monthly basis. but during Aug-Sep GSTR-1 we mistakenly missed Sales figures of Aug-17. We added Aug sales figures in Qtr Oct-Dec. We had enough input credit in both qtrs. but by adding Aug sales in Oct-Dec qtr output tax liability increased. But our point is that We had enough input credit in Aug-Sep qtr, we filed Aug sales amount in Oct-Dec. then why sbould we deposit Tax (ETO issued us notice to deposit Tax for Oct-Dec qtr) We have filed correct GSTR 3-B for all months. Only GSTR-1 has been filed wrongly. 
Pls help us.