How to prevent encroachment of land

My neighbour constructed pillar in boundary wall and about to construct wall in ground and first floor. as he constructed pillar in boundary wall without leaving any space /setback as per govt rules, i told not even a thread he shouldnot construct anything in my area as he erected pillars in his boundary wall where his area is completely over. now he asked me to use my area/land to cement wall by placing temporary sticks so as mason can able to cement wall. i told not to use my space/area to cement his wall since he constructed in boundary wall and his boundary is over and my area starts. now he forces me with local politician & lawyer that i have to give permission to cement his wall from my side. i said no as his boundary is over.whether they can legally make me to give my area to cement his wall?also neighbour saying after erecting boundary wall , pillars his area of 1 feet is still there for him in my land. he tries to cheat me .i have documents to prove my land how to stop him?