Parking dispute with neighbour in builder floor

I purchased a 100 sqyds builder floor in Oct 2020. Building comprises of UGF, First Floor and Second Floor. There is a 50 sqyds flat in parking area. As per my sale deed I paid the cost of 25sqyds parking area. UGF, Second Floor and that flat in parking area is owned by the same person. That person and his family have now started using entire parking area saying that I have only one car parking right and not 25 sqyds. They even object when I park my scooty there. They say that I can use only 1/4th of the parking area which comes around 10 sqyds after leaving common passage and stairs area. They say they have right to park two cars and one two wheeler whereas there is not ample space to park three cars thereIs there a legal way to get my portion of parking demarcated? And, can I challenge construction of 50 sqyds flat in parking area (of which they have registered sale deed)?