double sale of entire section of land to other party

I bought and registered plots of various sq.yrds in a section of N.A Land having survey no. 201, in Gujarat- Valsad District, by the then owner of that Block the year 2011. After 3years , I have learnt that due to some internal financial matters the then owner of the Plot has sold his entire right and interest and has also duly registered the entire Block / survey no 201 entirely to the new buyer. The new buyer of the Plot now threatens us and says that all my registered documents are not valid as he is the owner of the entire section of land and that he shall not part or adhere to the previous registered agreements by the then owner of the Land. Please suggest me the solution and legal implication and actions to be initiated, as I have put all my life savings in this and shall be stranded and also the legal advice, as whether, merely a name addition pending on 7/12 extract, for the plot owned by me and then this double registration by the land owner to the other builder ceases my ownership of plot to be developed on this piece of survet no and as to whether can I also initiate a legal action against the new purchaser of this Land. My agreement are registered in the year 2011, by then owner of the Land, as evident in recitle of the agreement and also government records. And then in the year 2013 this previous owner sold the entire land without plotting to the new buyer wide a registered agreement.