Registered Sale deed V/s Registered Agreement and bank Loan

Initially we got an affidavit from the owner regarding sale deep agreement for the period of 3 months and later on before expiry of the 3 months period we (two) jointly purchased a his build up house and taken possession immedatelyfrom the true owner. Earlier this was not mentioned or told to us by the seller i.e. the true owner. We got it mututed, we transferred electricity meter installed in our name, house tax also paid by us. NOC was also obtained form Municipal corporation before registry and we also took a loan to renovated the house after due verification by advovate of bank. After about 2 1/2 year, we came to know that the true owner has already signed a registered sale agreement and also taken loan from a private bank that approached to us while we were living in the house after taking possession. The person claiming having of registered agreement and full and final payment receipt of different dates in installments filed a court case to take possession. What should we do now. As they are also threatening to make invalid our sale deed on account of the their registered sale agreement. We also came to know that these people are money lenders.