Vat on constructed and oc received flat

Dear sir, I have bought a flat which was totally constructed and occupancy certificate was issued for the block in the project on which my flat belongs . When I booked my flat almost more than 50% of flats, the residents have occupied and were living. My payment terms clearly shows under VAT column 0 amount. I paid for total value, finished my registration, received my possession certificate also started living in it for past 6 months. Now my builder is saying he paid VAT on my behalf and is asking me to pay the amount. I have checked in various forums and clearly says that there is no VAT for buyers who bought a constructed flat and for which OC was obtained before buying the flat. The builder is falsely claiming. Please advise me. I purchased the flat thinking there is no VAT. I bought this flat by applying bank loan and now this additional claim by builder is huge and builder is definitely deceiving us. Regards Chitra prakash 9100382460