Dispuits of house boundry...

Hello one and all,I myself Anmol Rai from Sikkim just want suggestion regarding boundry.As we are small hemlet and comes under Municipality from 2010 as we have been resideing from 1993 till present;The land my Father owns from nearly 30 yrs above and it is legally registered but here comes the twist the neighbour purchase land from the owner which is hardly 40×50 and have constructed his building in 2011 and residing frm 3.5yr.The neighbour have put allegation that our house's roof water during monsoon has damage his house not only that his wife hardly 33yrs have challenged my Mother who is 50+ in her age,so we are two son who are out of station duty to job.Recently the government had decided to built pedestrian and for garage we decided to built entry passage from our boundry too but now they are against it and the areas comes under Road and bridge department and the Urban development and Housing development department gave us permission and in his presence it was done buy now he is claiming that it is his area and not only that he 2 or 3yrs ago dug the road ageing near our house which is under the Govt Deptt but didnt said anything from our side..we just asked the question that you people have consult us in good manner at that time also they challenge us to bring in court buy now everything has an limit we cant tolerate it is out of our dictionary and now they themself have send us legal notice from Lok adalt and has called us on 3rd of october 2015.So,could u please help me to overcome this dispuits legally by strong IPC Act. Regards A.Rai Sikkim