Sister fraudulently inserted her in name property docs. What to do?

I along with my brothers and family repatriated from Sri Lanka under IndoSri Lanka pack in January 1982. On our arrival one of our relative handed over the land belonging to my grand father showing its boundaries consisting of 2.25 Acres dry land. Out of which, we had documents in favour of my father for 1.50 acres. For the balance .75 acre there is no documents but we have been cultivating the land until 2006. Now we came to know one of our relative with the connivance of the land officials she has inserted her name in the Govt. Chitta and Adangal as she is the land owner, where my grand fathers name was there. How I should proceed on this matter. Kindly advise.