Someone sold me govt land.

Sir, In Jan 2016, my father purchased a 1200 square feet plot in gwalior, mp. But after some time he came to know that this is government property. So how the seller committed the fraud is as following:- 1) firstly he made a fake owner of land (by doing fraud he made the papers/document) 2) then he transferred the land to his name (he is having registry papers, having his name in madhya pradesh govt website and having digitally signed copy of that paper) 3) then he sold the land to my father. My father having the following documents regarding land:- a) registry papers b) papers of nagar nigam (my father pay tax every year) c) my father's name shown in online portal of MP govt- and having a copy of that paper. d) having electricity connection. My father already constructed house on that plot. So, around 20 days ago, we got a notice from Tahsildar about illegal encroachment of govt land. So I want advice regarding this. (Please include following points in your suggestion:- 1- are our documents sufficient for any legal action (knowing that all documents are authantic). 2- is there any possibility that govt can demolish our house & acquire the land (knowing that there are 50-60 houses in same situation))