itc of vat

No way for set off liability from VAT to GST without filling of TRAN.

as per the transitional provision (section 140(1)) of cgst act, a registered person is entitled to carry forward the cenvat credit of return filed immediate preceding the appointed date, his electronic credit legder (as per form Tran-1 ). I understand that you have not filed Tran-1 form, hence in such case you can't carry forward the VAT ITC to your electronic credit ledger for payment of GST.