Sale property deed with 2 lacs advance done on June 15th, 2011

Hello Sir/Madam, I'm a physician by profession and we bought a 200sq yard land around Delhi while my Dad was alive around 2005. My Dad died in an accident in 2006, and thereafer our land stayed unoccupied for many years. Around 2011, I was about leave abroad for my Medical training for few years, where I'm still residing in United states. Somehow, property dealers through whom we bought land initially got to know about my family situation where I was solely responsible for Aquisition/selling of land. Property dealers and local guys keep calling me and threatening me that our land will be captured in my absence and I will never be able to take possession of the land. Finally these property dealers and one buyer came to my house for conversation and told me about all the grim situation of all this, and made a Sale agreement with 2 lac bayana that we accepted. Within a week, we realized that whole deal was under huge pressure and market value of the land is way higher than what they offered us. I contacted property dealers and the buyer that we don't want to go ahead with this deal. Buyer has persued a court case against me that I'm violating the sale deed. Agreement in nutshell says that in Seller has to pay 4 lakh back and whole period for paying whole land money, 15 lakh was 9 months. I have intimated buyer by registered post within 2 weeks that I don't want this deal, and mentioned particularly that this whole deal was under pressure and offered to pay back his 2 lakh. I'm currently abroad and my mothers is persuing case in behalf of me with a lawyer, property dealers have presented 3 witnesses under oath and my mother is alone there. I want to ask what other measures I can take to make my case strong and prevent my land from these land mafia there and if possible to protect my land through court of law. What is harshest penalty I may have to go through after final court order.