First thing Whether you are talking about Land / Land and structure above / Some Flat , building - Not sure 100%
From wordings I make out Land
Well Land laws differ from state to state as each state has its own land Revenue Code but procedure are almost same
Generally Land record dept. maintains site measurement etc. Private measurement are not valid as such . So measurement which you mentioned or dimension mensioned in orignal registered deed you have to check whether it was govt. measurement or private
Since you say you have existing wall. You should immedately take Injunction from Court , telling that wall should not be damaged or changed. And other person should not cross the wall till the issue of area or dimension is clear. This you will get if proper step is taken within even a day. Showing urgency clause .
Question remains area of the land. It mostly depends which kind of measurement is stated in registered document . Govt measurement or private . If Govt. measurement then you are compartively safe.
If Private measurement then the area of land which you have you can claim ownership and or more land which may be with you as adverse possession against other party
At similar time the wall which is exisiting if it exist and injunction is there then you can clam that dispute have to be taken within specific time under Limitation act else it is waved off . Now previous owner have waved it or there was no dispute hence Under Limitation act his claim should be dismissed. It is generally 3 years only . So on Limitation act basis you can claim benefit additionally If you have more land you should claim adverse possession.
Again most imp. if it is land then what govt. measurement says and what govt land record says ? This is also very important rather it will decide the fate of case
