Police not registering fir for illegally occupied property

I would suggest you to approach an experienced lawyer and he will guide you properly. You can sue the people who have acquired your property illegally since you have all the records and you can write a complaint letter to the SHO of your area. I'll still say you should hire a lawyer and he will guide you through everything. Hope it helps.

For immediate remedy, approach the Executive magistrate of your area under Section 145 of the Criminal procedure Code, and thereafter file a declaratory suit in civil court  to determine the title of the property.