Export refund

I export some goods for the month of july,2018 with payment of IGST tax , for this purpose I filup GSTR1 (Table No. 6A) & also GSTR3B { 3.1 (b)} schedule return for the Month of July,2018. but refund not come , Custom depertment said some mistake in return . Can i will  gave  Revised GSTR 1 Return or Fillup RFD 01 A RETURN...............