Service Tax & VAT Rules Clarification

We have Purchase the Flat in Bangalore from one of the reputed Builder , We would like to know about the Service Tax rules (Before the GST implementation) :- Occupancy Certificate applied by Builder in the month of May 2016 and the received the OC in the month of October 2016. We booked the Flat in the Month of 30th June 2016 and paid booking amount. We have performed the Agreement in the month of 14th July 2016 Some amount paid in the month of August & September 2016 App. 82 Lakhs and paid service Tax app. 1 lakhs + Remaining amount Paid in the month of December & March 2016-2017 respectively and paid service Tax App. 3 lakhs + VAT App. 7 Lakh Our Flat registration was done on 30th March 2017. We would like to know the flowing In what condition Builder Can't charge the ST & VAT ?:- (A) When the Builder has applied the OC in the month of May 2016 that mean Flats was ready to move condition and construction was completed then how can builder charge the Service Tax & VAT amount from us ? (B) When the Builder is received the OC in the month of Oct 2016 that mean Flats was ready to do the registration then how can builder charge the Service Tax & VAT amount from us. Please guide us after OC applied or OC received whether Builder Can charge the ST & VAT amount ? Regards, Sanjeev ([deleted])