Land litigation

Hello Everyone, CASE STUDY - I have one acre of land which is facing to the road horizontally and the one who is at the back of my property is trying to Acquire the half of my horizontal property and trying to demonstrate that I have one acre of vertical property. The problem here is the whole land of both of us is on same survey number and seller is one. However, I am the first buyer from the seller and I have sale deed registered and dated 10 years prior to other party. The sale deed of the other party is also showing that he has a way beside my land of one acre from the road to enter his bit of land. the other party is demanding us to leave some portion horizontally and to accept a part of land which he is willing to give from his share of land so that my land bit looks like vertical facing to road just because of the reason his document shows road facing way. My question here is: Is this a fraudulent sale made by the seller to buyer without disclosing facts about my land of one acre which is horizontal towards the road. OR Is this a fault from the buyer for buying a portion of land which is already sold. OR BOTH would be sued in the court of law if so under what provisions or clauses they would be sued either separately or combined. PLEASE CLARIFY