Is There A Way To Own Govt Land?

A man sold us 5 acres saying it was theirs and by the time we went to register that we were told it is Govt land. We applied for registration and got injection and permission to construct in that land. After 15 years, the one who sold us returned and tried to grab the land, saying he never sold it but gave it for lease. Not only this but for past 4 years he has been getting people and disturbing us and fighting, abusing and building rooms in our place. He shook hands with local police and Revenue department and is pulling us into the station, behind bars with false accusations. How can we deal with these people?