Construction halted by Police

I have a land and a house of combined area of 2500 sq feet which is registered on my mothers name out of which 1500sqft land is empty and we can use it for our purpose the land was bought by my father from a family of 4 members who had a partioned amongst themselves as a family and they amongst themselves compromised that the 1500 sqft area will not be used for any construction purpose but the land shall belong to the partner from whom I bought the land and not in the joint property of the family . we bought the land and 1st floor 3bhk flat from that partner and my neighbour the ground floor from another of the 4 . The partner from which I bought the land gave me all the rights over the land and flat and we registered the land and flat separately now problem has arised that my neighbor who isn't any of the partner or relative of the family from whom we bought the land resides on the ground floor has put up a complaint that I am doing an illegal construction and he himself constructed a hall in the space allottedd to him adjacent to my land and opened the gate on my land, on asking not to do so he started fighting so we had to put up a boundary and close off his gate. they went to police station and complained about illegal construction The police comes and asks us to stop the construction nd harrasses us . My neighbour is SC ST by caste and we are of general category he always threatens us that if we do any construction he will get us jailed in SC ST act his some relative is there in the police and the police is also trying to extract money from us and we are left in a helpless position.