Registry done without owner's consent

My father was in need of money 3 years back when a person came to help us and told us that he will make an agreement and will lend us money and he gave us the amount of Rs 13 lakhs and my father duly signed the agreement for it but he never gave us copy of agreement papers. Then 11 months back we got to know that he has made sale deed with that agreement and showed us that my father has sold the property to him in 25 lakhs and he has paid whole money (which we have never got)also we were not informed about this i have a buyer who is ready to pay 35 lakhs to us and is ready to buy our house.we are in need of money as because of this person we are already under soo much pressure and as my father is physically and mentally disable we are in need of urgent money. Is only registry sufficient to own the property?can i sell my property to other person because as per previous person haven't made the full payments not even he considered our old property papers which are already been mortgaged by nationalized bank?how can a person register the property on his name without original registry papers?