Neighbours creating problem at my land plot

Hello Sir, My father owns a land plot in bokaro steel city. He bought this land 31 years back and also got his aadhar card no enrolled with the same address. All neighbours and people know us in the locality., We have built boundary walls around the plot and small shelter. My father is a retired person and is in his 60s so he is unable to cope up with these disturbing elements. We are living in bihar right now and becomes difficult to follow up these. A new person has bought a land plot to the left of ours. He works in a bank. Recently he destructed our boundaries of left side and built his boundary in our plot. He also threatens and trying to take over our land. I doubt one of his neighbour is provoking and involved in this. I have also come to know that neighbours' land is under some legal problems perhaps sec 144. What I am looking for is the assurance of no more such activities on my land plot and security to my father and property. Please suggest with some legal and appropriate steps to be taken in this regards ASAP. Thanks in advance and waiting for your valuable replies.