Stilt parking occupied by builder

Hi all, I am murugesan from chennai. In 2015, My father decided to buy the flat and finalised registered in chennai. Actually that building plan approved by tambaram municipality on behalf of CMDA for G+2. As per plan Ground floor completely stiltparking and first and second floor having 3 flats each. After completing 90% construction work, the builder started to sell the flat. builder constructed the 1500 sq ft flat in ground floor without approval. all the flats not sold immediately. its takes nearly 2 years and no one jointy purchased everyone purchased 3 to 6 months gap. all 6 persons purchased in different time. no one met with each other before purchase. Here only builder played well with all. At the time of price negotiation he told "car parking only for 3 persons" to every one. remaining space after his flat in ground floor suitable for 3 cars. so no one raised any query. He not mentioned the dimention of car parking in construction deed. He specified as "Car parking will be provided" in agreement. Also he gets sign from my father in the no objection declaration on 20 Rs stamp papers. He sentenced like on that 20 Rupees paper "i am keeping this portition for my own purpose. We(me) know the building in ground floor and we don't have any objection.we will not claim any legal claim in future." My father checked with the banker regarding the ground floor portition. they told that there is no issue to your portition. you can go a head like. After all flats sold only, we found parking given to all 6 flats. we all approached the builder. He is not responding and telling that i can't do anything. go legally. He did the registration (by giving bribe to SRO) of ground floor to his wife name without any approval from CMDA after with in 30 days from last flat sold. and he changed the EB Connection also to her name. Because of this my father feels disappointed. He is 60 years old. Kindly anybody give your opinion