Land dispute

my fathetr bought A LAND IN WEST GODAVARI IN 2001 WE DONOT HAVE ANY LINK DOCUMENTS. THE LINK DOCUMENT NUMBER IS NOT MENTIONED IN THE SALE DEED . IN 2011 ANOTHER PERSON SOLD THE PROPERTY WITH DIFFERENT SURVEY NUMBER BUT MENTIONING THE SAME BOUNDARIES NOW THEY FILED THE CASE BEFORE JOINT COLLECTOR. SINE 2001 WE HAVE CONTROL AND POSSESSION OF LAND, ANDANGAL , 1B , AND PATTADAR PASSBOOK AND TITLE DEED ALL ARE IN MY FATHERS NAME. SINCE 2001 TO TILL DATE WHAT TO DO NOW. THEY ARE NOT PRODUCING ANY LINK DOCUMENTS ALSO