property

I have bought a flat on loan from ICICI..in vashi..there are 2 wings in the building i have a flat in the B wing, on 4 th floor...there are 2 builders who made this building known as victory residency... one of the builder is staying in my wing and he owns all the flats in the B wing except mine... Now he is pressurizing me to sell my property in a lesser price then the market value... he is not allowing me to keep any tenants in the flat.. now luckily i got a family who is staying in the flat on lease they are my friends family... he is harassing my tenants my switching off the lights from the switch board by not supplying the water and so on..it is been 2 months they have come and in the first month he hit brutally to my friends family...they filed a case against him but still he is continuing the harassment...today they went to the police station again to inform the police about the same...The builder is telling the POlice that he is the owner of the flat and te tenants are staying without his permission overthere..now the inspector is asking for the property documents ...what should I do.