Plot sale agreement on a 20 rupee stamp paper

Hello, I have recently entered into an agreement with a person to buy a plot. In this regard, me and the seller of the plot made an agreement on a 20 rupee stamp paper (stamp paper is not on my name, rather on of my friend gave me) by paying an advance amount of 2,50,000/- (60000 in cash and 1,90,000 via online transfer). Now i came to know that the layout is not approved, so asked the seller to return the amount for which he is denying. Can i go for a legal case against him. what are the Pros and Cons . Can someone help me out in this case.