Cheating Against residential Land & not paying my money back.

My brother in law's cousin brother approached me through my brother in law about their money Problem and he mutually agreed with me to sell his extra residential plot land (amount Rs:600000). he also agreed to take the money in instalments. I paid him Rs150000 in cash (by taking a personal loan against my small job) in first slot in presence of my bother in law & wife of the party(land owner). Now no record of transaction of money is maintained as the deal was in cash. As the person was good in my eyes before this incident , I blindly believe him. I also cleared him before this money transaction from my side that I will pay the rest money in definite time interval (clearly mentioned him & his wife in presence of my brother in law) as I am preparing for civil service ,I did not want to be disturbed in middle. They also Mutually agreed to my Condition as their financial situation was not good.After two months of this deal again they approached me(which is not the time given by me) & I told them that now I am not able to pay. Then they suddenly turned back & told that they will not sell land as it is not beneficial to them & they will return my money in between two months. I also agreed to this condition. but 9 months passed they have not returned my money& giving so many false promises & timing to return money. My bother in law is coordinating from both sides keeping in mind the relationship , but result not effective . But party has given a hand written letter to my brother in law (In my Ignorance) that he will return the money when he will get the money from their Land acquisition case from coal mining company. Please Suggest me what legal actions should be taken in above situations & how to recover the money. The party earning around 15000p.m from agency job