Help wanted against act of neighbour affecting our Property.

I will be grateful if I am fed with a suggestion on my following property related problem with my neighbour. We two brothers are presently the owner of a residential house under the municipal authority of South Dum Dum Municipality. Our neighbour who bought the property a few month’s back, after buying the property in meagre way started illegal extension with encroachment and for that they are influencing the local politicians to avoid any sort of counter objections. Now they have devoted to dig up a drain across our main entrance which was never felt for the last sixty years of our residing. Drainage facilities of all the residence in our locality already exist including ours and theirs. Now for their own benefit they wish to dig a drain in front of our house to get pass their water tank overflowed water which if they need, though can well do that by digging a drain across their house but to maintain decency they dived to dig the drain across our frontage. To make understandable their house is a cornered plot and can get their drain connected to the main drain from both side. One by digging across our building frontage and the other by digging their own front. Now for their maintenance of their house decency they initiated and influenced the local municipal councillor, obviously by political influence to dig out the drain across our frontage. They diplomatically initiated to get the work done by the Municipal Authority themselves instead of on their own, with the help of the local councillor, which is through their own political platform. Under the circumstances I will be obliged if I am being guided with a rock solid advise as to what I should do to protect my interest. Solicit immediate kind guidance. Best Regards, Sibsankar Datta