Documents required to prove that flat has been transferred to me

Hi, I own a land in Pune. Its a common land owned by 50 people. We had a registered society formed among the members. Our society chairman/secretary has a connection with a builder and forced us to gave our land for development to the builder. (this was in 2010). The building is now ready. I have been provisionally allotted a flat in the building, however never received any allotment letter from builder/society. (its just verbal allotment). Light bill of the flat still carries builders name. I have my 1. Share Certificate 2. Builder agreement with the society( no individual agreement was done) 3. 7/12 document What all documents i should get from the builder / society which will prove that this flat is mine. (both builder and society chairman are thieves) Thanks.