Land illegally occupied and they have the original sale paper

Hello sir, my name is . My mother has 2acres of land at BUDIDHA GADDA PALLI village, GORANTLA mandol, anantapur dt, AP. Sir, we sold our land a party in 2003 for 65000rs. Agreement was done on that day and 10000 was received from them. Agreement expires in 6months. Due to some problems they failed to do registration in time. We asked them to do registration even after 3years bt they didn't do. Now land value is raised to 12lakhs. After 14years they are asking for registration for the same previous amount 65000. Agreement paper is with them only. Now we are not ready to sell the land to that person for the less amount.. he is opposing us not to sell d land to other person. We sent notice to him but he is not responding and at the same time he ploughed our land for corn cultivation. What should we do now sir.