Patta name transfer in coimbatore

Dear Sir, My Dad purchased a house 20 yrs before, but failed to get Patta transfered in his name. The property land belongs to Natham type and the patta is in some X person name which nobody knew and even we traced EC for 30 years no such X person name came up. We approached VAO, they are asking for a written No-objection letter from that X person which is impossible to get. We doubt by mistake Patta name has been transferred to the X person. Without that letter revenue department people are not even responding. Please help us ..on how to get Patta name transfer to my dad's name from that X person. We have all documents in my dad's name for around 20 years - Sale deed, property tax, EB Bill, Water connection doc and bills, etc.. Thanks!