Dispute on Purchase of a Plot

Sir, I have purchase a Plot from a Seller X with proper Registration at Sub Registrar Office with proper sell deeds with payment of appropriate Fees . But I have come to know that The Seller X was made an agreement with Notary with some other person i.e Y 2 years before to sell him the Plot after he (byer) clear the loans of the Plot. But Byer was not cleared the loan and this matter also not informed me by the Seller . Now the Y is calming that the Seller X was committed to sale him the Plot earlier and has Notary agreement with him. Sir kindly guide me what to do ? Will I responsible for any wrong thing here and the Y who is claiming that he has an Notary agreement with X for this plot is authorise to stop me to do construction work on it. Please advice me the Validity of the Notary Agreement and position of mine in this sale. Will I am a Looser ? Or I am correct as I have follow the all right procedure to purchase a plot but the seller has cheating another person for which Will I be responsible or Seller?