Can i cancel the reistered agreement of sale which was executed on december 2010

Sir i am a businessman, due to some business losses in the year 2009-10 i was getting help from a person whose primary business is money lending whenever i need money. One day i got a big order in the year 2010 December and i need 3 lakh shortage to supply the material to my client. As usually i approached that money lending person and asked him to help me. He asked me collateral security for his money and asked 30% per annum interest. I agreed and executed agreement of sale and the money lender registered the documents from local sub registrar office. I was giving him interest per month and also giving every month a part of his principal amount. Within 2 years i paid regular interest and also i succeeded to clear full amount also within 2 years. After 2 years i called him to cancel his agreement of sale, but he denied to cancel and till now since from 2012 he is not coming to cancel the same. simultaneously on the same day my younger brother also took 2 lakh and he also done same areement of sale. In the year 2015 the money lender filed a suit on my brother that my brother was executed agreement of sale and he has to register his plot in favour of money lender. In the year 2014 i sent a lawyer notice to cancel the agreement of sale but he did not replied. i have the register post receipt. now after 8 years he sent a lawyer notice to me that i has to register my plot in his name taking balance amount of 1 lakh. sir my plot value is approximately 50 lakh rupees. now shall i send a letter to sub registrar officer and ask him to cancel the 8 years old agreement of sale which was done only for collateral security. my mail id is [deleted]