• Land matters

I own a four-storied building over 6 poles of land. When I purchased the land back in 1990 , there was a vacant land at the west side of my land and everyone in the locality knew that the owner of the land had shifted somewhere else never to come back again leaving the land behind and without selling or gifting the same to somebody, so the land was taken over by a Trust.
During the AILA cyclone of 26th May 2009, a landslide occurred in a part of that land attached to my building causing a threat to my building. So informing all the local authorities I constructed a wall in a part of land attached to my building for protection and safety. Nobody claimed that the land was his or her and came forward to construct a protection wall at that landslide-hit area.
Now, suddenly a third party has emerged and claiming that they have purchased that land from some other person who has neither purchased the land nor was he gifted the land by the original owner
. Third party is taking initiative for construction of the building and I am sure they will certainly cause damage to the wall which I had constructed before 11 years for the safety of my building and has been looking after the same since then.
Under such circumstances what should be the line of action from my side? Please guide / suggest.