Brought land from a person now 3rd party is claiming that land

A man sale me his occupied govt. Land with his signature on stamp paper 2003. I build there house with proper electricity connection and inhibited there from 2003.But after 12 years the real owner of this land come and he said that this is a miyadi land on his fathers name. Now he force me to leave the land. Now what should I do? Pl. help me.