Procedure to challenge ownership rights and proper registration

 i am a hindu by religion. i have a property in mahabaleshwar, my dad did complete the documentation of the property, all the while maintain presence on the property, i have a aunt who also has a bungalow just adjacent to mine. now the property has been shown in someone else's name. i want to put my name on the documents and revert any false claims to my land. my initial attempts to contact the person who sold the land to us have been fail. i only have purchase letter which has my fathers name on it. the date on the purchase letter is far older than the date which is said to be registration date of that land in some other name.in short i have a more older claim than the new occupant. the site is still undeveloped.