Double registration of a vacant property

I purchased a land in 2003 . I serveyed the land with the surveyor and made a compound wall till date . I constructed a small shed & taken electricity supply also . After so many years last year one person came & showed the documents & his land is mixed in my land . When I checked the documents , it is registered in 2002 year . In his documents also the person who sold to me is only signed . The person who sold to me only signed in his documents (2002) . This is a ansisters property . In my documents , the person who sold to me & his sons also signed . But the other person document(2002 registration), only one person (father) only signed . I asked the person (2002) registration , what where u doing so many years of not securing the land or enquired about the serveying . The person who sold to us is passed away in 2007 . The land is in my control only with the watchmen . But 2002 registration person is threatening me to handover his land . I told them please go the person who sold to you or his sons , they will give u the reply. But he is creating a problem in my property by throwing stones of the compound wall (fence ) . Please suggest, what to do .