Defamation

“Is defamation suit by a fraudulent person valid” I did not know the fraudulent motive of my own RELATIVE (Mr. Baburam) who is also a discreet “land-broker” in Siliguri. On his repeated persuasion and TRUSTING him I purchased a plot of land in Siliguri in 2012. (He was formerly from Shillong and shifted to Siliguri in 2010, so I trusted him). It is only 5 months back that i learned that particular plot of land is "Flood-prone" area earmarked by the West Bengal Government as SIKISTI BHUMI where no concrete structures can be constructed. I had purchased that huge plot (1 biga and 1 katha) for my residential purpose but I now I cannot construct RCC building). I repeated requested BABURAM to return my MONEY with "interest" but he did not listen to me. Since he did not resolve my case I was shared about his fraudulent activities and how he cheated me through FACEBOOK's "closed group" But now he is going to file DEFAMATION Case against me. He has also cheated other families who are his relatives. I have records of phone conversions of the aggrieved victims which clearly indicate fraudulent character of Baburam. Please advice me how to go about.