18% GST on maintenance by Runwal Builder and MVAT rebate for the balance amount

Hi Mr. Ajay, I would like to seek your advice on a few of my concerns and would appreciate your kind support so. 1) I already MVAT on the whole amount of the Flat basic cost before the GST came into effect and later I continued paying the GST on the balance amount. My query is, how can I get the rebate or discount for the additional MVAT component that I paid as an inherent part (VAT+ST) of GST on the balance amount. So, in short, I should get back the pro-rata VAT amount for the balance amount for which I had paid the GST. 2) Builder is asking for 18% GST on the fixed Flat Maintenance amount of 1,30,000 for two years. The demand was raised on 18/03/2019 but I have not paid yet since there was some issue in the demand which they had rectified later. Plz advice how much %GST I am liable to pay with and without ITC. Does it incur a deduction of 1/3 of the land amount cost or not? 3) The builder has claimed 18% GST on Proportionate shares of property taxes, water taxes etc., and Legal and Society formation charges and Shares Money etc. Plz advice whether it is a legitimate demand. Does it incur a deduction of 1/3 of the land amount cost or not? 4) Is the contemporary GST laws applicable or the old law i.e. issued before 31st March 2019 is applicable? [deleted].