Seepage Issue from Upper Floor and No Cooperation from flat owners

My house(DDA Janta Flat) is severely damaged due to the seepage from the pipeline of the 1st floor. Our ceiling and walls are badly dampened & destroyed by the water seeping throughout the house and we made several requests to the upper floor flat owners to get their blockages cleared and pipelines replaced / repaired. Our ceiling has fallen off at a lot of places and because of this we moved out of our house and are now staying at a rented accommodation in the same locality. We have been repeatedly reminding them to do the needful repairs at their 1st floor and renovations of our flat because of the damages caused, however, no concrete action has been taken so far regarding the same. Due to this delay, we have already suffered loss of our possessions stored in shelves such as books, photo frames etc. which were deteriorated as the seepage has spread to a larger extent now. The 1st floor owners are non-cooperative and simply refusing to comment. As per our last conversation with them, their attitude seems to be steering in the direction where they don't want to bear any expense of renovating our flat. We cannot bear all the expenses because due to their delay, the extent of damage is too much and it's costing us a lot of money. We have tried speaking to them through RWA also, but there's not much use. We also made a complaint to the Office of Deputy Commissioner , South Zone, MCD stating the situation. But when we enquired further on the update of action, we were told that this will not be under their authority and there is not much hope of acton from their end... they advised us to talk to flat owners for amicable settlement. But that of course is not working for us as they are not even discussing in line with the expenses for our flat. I would like to know a few things: a) Is there any other authority / office I need to approach with the complaint who can put some sense into the flat owners to bear the expenses of our repairs as well? Ours is a DDA Janta Flat is in South Delhi. b) If nothing works and we have to send a legal notice, what documents / assessments would I need to prove that the seepage is because of their 1st floor bathroom pipes and the extent of damage is due to the delay from their end? Keeping in mind that they might not cooperate if we need to take assessment of their flat, they might not be willing, please advise. c) If they still refuse to do it in spite of legal notice and I have to go for a court case, how long does it take for such cases to be settled because if the legal expenses / timeline is going to be more than my repair costs, it would not be an advantage to me and ruling being in our favour will largely depend on what we can prove and what all will be needed to prove it? Sorry for such a long query.. but I wanted to put across all the details clearly and the doubts hoping to get some clarity in the matter.