- Your contract is based on payment linked.
- GST came into force on 01.07.2017. Firstly, GST can not be applied on June demand letter. If the payment is made in July 17 then you were required to pay GST@12%. Might be they charged GST@12% from you and paid service tax to the govt.@ 4.5% of 1st installment.
- If you see overall, GST@12% on 45.70 lacs comes to Rs.5.50 lacs which is justifiable. As the first demand letter is of June 17 so GST can not be levied. Also as per demand letter, service tax is levied on 1st installment.
- If you are questioning on ITC benefit transfer then you should have proper working before GST and after GST.