Fraud - Sale deed

Dear Sir, I have grandfathers agriculture land of 10 gunthas which possession till date with me. above said lands 7/12 extract in 2009 was in the name of my father and his three sisters but it was replaced by my grandfathers relative . We enquired about it we come to know that my grandfather made sale deed on 19.03.81 to him (relative) against 6000/- Rs. but also made reverse sale deed on same deed mentioning that above rs will refunded by grandfather in five years or land will be acquired by him through oringinal sale deed.So, my grandfather refunded his 6000/- in cash on 16.04.85 to him but he provided the receipt for land giving back to u and money receipt but he didnt signed it . He have intentions to deceive my grandfather due to his illiteracy. So it was back in time as my grandfather paid him he take charge of land till he died in 2004. then my father & his sisters name registered after his death on 7/12 .But in 2009 he produced original sale deed in talathi/tehsildar office and registered his name in 7/12. We enquire about this to him personally then he said no money received from my grandfather and there is no sign on receipt .So, he is saying i can take any time possession of this land due to good relations with my grandfather i didnt take possession till date.