Complex situation

A Plot of a person was mortaged to Nagarjuna Finance . I entered into an agreement to buy it in June 2018by paying an advance of 20 Lacs by NEFT and also cash as per the time frame in agreement. copy of this agreement was submitted to Nagarjuna finance I got a letter from Nagarjuna Finance that balance amount to be paid and that when the amount is paid original documents will be handed over to me and seller will register the plot in my name . Seller also signed this letter as an acknowledgement. Seller avoids me and refuses to come to FInance office so that I can make payment and receive original documents. meanwhile seller defaults 4 payments to Finance company even though I transfered 2 payments to his account so he can pay Finance company. Nagarjuna Finance proceeds to take posession case filed in Chennai and order served in Jaipur sessions court. In the same court in which Nagarjuna Finance case is going on I filed papers with my case and willingnesss to pay Finance company . Agreement copy submitted in court. While this is going on seller silently enters into a deal with 3rd party and pays up Finance companies dues and gets plot registered in his name. Case is still pending to which I am a party. I contacted new buyer and he says he is unaware of all this and would not have bought if he knew this. What do I do in this situation?