Servey dispute

Since 1954 my father is the owner of the father died on 26th may 2016. in december 2017 one person came to us and asking give 2 acre land from our land survey number 106/2 with an extent of ac.4.12guntas.he is saying that my father executed sale deed long back in june 1971, but the land survey is 107/2 in the register document but my father never owner of that survey number, our survey number and registered survey number is not matching.we don't know whether my father did this sale deed or not. in his life time nobody asked for they are asking what shall i do.