Lessor sold land without NOC from Lessor

Sir Our company had leased land for setting up petrol pump and appointed one dealer (both different person and different agreements). After few years one more person was found active in the pump and started malpractice. The dealership was terminated and we appointed another person as temporary ad hoc dealer. During obtaining statutory license for new dealer, it was found that the land was no longer in name of our lessor. Instead he had sold the land to other person(one who caused malpractice) We have registered lease deed but mutation not being observed. District administration says they either need lease deed with current land owner or some NOC from him to let the petrol pump operate. The new land owner is not a gentleman and very difficult to talk to him. Also he has refused to cooperate and instead threatning that he will lodge case against company to vacate the Land. District administration says that they don't care for original registered lease deed and we may file case for fraud against original lessor. This lessor is now untraceble but was happily receiving lease rent through bank right till now. Company has invested huge amount at the site and if fault of our people is found then few heads may roll. We don't know how to proceed and against whom should we file case. Also the new land owner is physically stopping us from entering the land and says that it is his land. Please advise