illleagally taking possession of house

1) it is purely civil matter police don't interfere.2)file suit for eviction in civil court as he is illegal occupier .3)yes you can sell your house .

Oh. That mean any one can illegally take possession of any one house .

I m surprised that there is no law to stop this. 

What are other way to stop this 

 unlawfully remains there with intent thereby to intimidate, insult or annoy any such person, or with intent to commit an offence, is said to commit "criminal trespass". You can file a criminal complaint to the superintendent of police of your area. 

If they were staying in ur house legally than it was in their possession else it is in ur possession. 

So as mentioned by you if possession of ur house is taken illegally from you then it is criminal trespass as per section 441 IPC.

Also check local laws for criminal trespass e.g. UP state law states specifically that with intention of taking unauthorised possession. Then you can file an FIR with police.

Else if possession was with them Then you need to go to civil court for eviction notice.

I have put a tenant in my house , they threatend the tenent to vacate the house, that time I have made a complaint in local police , police has registered a NC for 506 . 

Next month the tenant vacated my house , I put my lock on the house, but I my absence they broke my lock and take the possession of my house . I went to police stn to complaint of illleagally taking possession of my house. But police said that it is a civil matter and I should approach the court for this .( The house is in Maharashtra state ) .

File private complaint  in magistrate court against police court will direct the police to take complaint.

This is certainly a criminal case. Talk to your local SP and ask him for help in this matter.

Also police can't register a NC without magistrate recommending them, did you visit magistrate last time? This time also you can go to magistrate if police doesn't register even after meeting SP