Builder trying to sell parking space allotted to me to someone else

I purchased a builder floor 6 years ago. Building has 4 floor and 8 flats in it. Purchase Deed says that I own proportionate share in the stilt parking. Builder is trying to grab my parking slot claiming that he sold that parking to another flat owner who bought the flat 2 years after I bought my flat. I have been using my current parking ever since I shifted to this floor. Builder and my new neighbor are trying various tactics including threats and goons etc. to force me vacate my parking space and shift to another parking space which is too less without proper entry. What legal options are available with me? Please guide.