Land dispute with the adjacent landowner to our apartment

Hi Sir, We are from the owners association of Candeur Rise apartment in Varthur Bangalore. Need your help\suggestion on a land dispute issue going on with the adjacent landowner to our property. The adjacent landowner claims that a small portion of our land belongs to him and he is trying to attach that to his property. In order to do this, he has to demolish a portion of our boundary wall and he as already informed us that he will do this pretty soon. He has got a land survey document from the bhoomi portal supporting his claim. We don’t know how legitimate this document is as we were not part of the survey he has done. We have done a privet survey and as per that, his claim is not true. We have already approached the builder however they are not ready to interfere. Or only as is to get a proper survey done including both parties and we are ready to give any portion that belongs to him as per the survey. Appreciate if you could help us here. Also please let us know your fees to take this forward.