Leakage issue and harrassment by neighbours

We are facing leakage issue in our flat and same is faced by the people staying below us. We are staying on 2 nd floor and the people staying at 1st floor nd ground floor are also facing the leakage issues. Now the problem is that the person staying below our flat( 1st floor) is blaming us for the leakage issue which cannot be true as v also are facing severe leakage issue v are considering probably from above flat but the person staying below is adamant that it's caused by us and harrasing us and picking up fights every now and then. The secretary also answers diplomatically and doesn't try to solve the matter inspite of repeated requests and will only ask us to fix the problem. All in all many people have ganged up against us claming that it's our fault and v should fix it but even v are facing same leakage issue nobody wants to here that. We are just exhausted living like this and frustrated as our mental peace is taken on ride by the person staying below. We want to go in a proper legal way to give him lesson that it's not our fault how to go about this. How to complain and to whom? Kindly guide thanks in advance