We are Pvt ltd co in Mumbai. In one of our export invoice in shipping bill copy Invoice number is mentioned as EXP/18-19/023 whereas original invoice number is EXP/19-20/023 . We have not yet received refund of IGST tax for the said invoice. The SB code is SB005. Please suggest what action should we take against the said issue to receive refund. Invoice date is 06.09.2019. GSTR 1 and 3b has been filed for Sep 2019