Obstruction by neighbour while doing construction, what to do

I have a house built on a plot. I want to do plastering of backside of my house and for that I need to make bamboo structure and some portion of that structure is in front front of their house. In actual the neighbour has made a boundary on my land because I didn't give boundary after purchase and they took the advantage of it by making stairs and boundry wall from backside land their wall and stairs have encroached my land. I ignored that also. Now, 1. Neighbour obstructing the work of my first floor and backside plastering. 2. Askinge to remove window which is erected on my wall at backside. 3. Intervention of local police which neighbour got by giving written complaint against me. Please let me know the way ahead and what is the role of police is this case? Is this a civil case or can police call the parties to police station? Also, how to get the measurement done of land so that I can claim my land? I will be very grateful to you all. Please help me.