Fradulent forgery of plot situated in my father patta land in village.

My father is the owner of 10 acres of land in my village and my father is educated &bedridden recently and one person falsely created a fake sale document with a thumb impr dated 2016 alleging that my father has sold 2 guntas of plot from his land and that person did his family settlement by adding 2 guntas which is adjoining his previous house area and did registration of his family settlement to his son and now he is creating nuisance claiming that he had bought the 2 guntas from my father.