Sold illegal / Govt. Property. Telangana

Sir Good Afternoon I am NRI, my parents living in Telangana came from poor family , i bought a land in Telangana costs 15 lacs, due to my parents are uneducated the mediator and the person who sold the land was told the land was genuine.The land was registered on my name 2 years back. My parents constructed a compound and a room, got the house no. with in 6 months only the collector came and demolished the room and compound because it belongs to lawan land ( means the govt is given for the poor people) but the seller and mediator cheated my parents. From 2 years my parents are going and coming to the seller, he is saying all the stories.They went to PS but they are not taking any interest ,3 weeks back my mother got heart attack due this tensions , she is sick right now.Can you please suggest what legal action has to be taken against him and mediator for selling these Govt. lands. They are doing these types of business from so many years , they are intentionally selling the property who are uneducated/ unknown people.Thank You.