Basement floor illegal construction (office in the place of parking).

I have purchased a 2 BHK flat in a residential apartment at Hyderabad 2 months back. The builder got the OC from GHMC and handed over to us. After getting the the OC he started construction in t he basement floor, which was meant for parking only previously. He along with the basement parking owner they have constructed 1 clinic and 1 office. Now they are saying as they have compromised between them after adjusting the parking spaces. When we ask they are arrogant and giving threats, as the Land owner is IT commissioner. Kindly help me in tackling the situation.