Liability if there is water leakage from upper floor

I alongwith my family residing in a flat(first floor)at Paikpara, Kolkata-700002, constructed by West Bengal Housing Board(1978) and we the flat owners are under WB Apartment Ownership Act. Our outlet pipes are inside the Flat. For the last one year water is leaking from the floor/pipes of upper flat(2nd floor,just above my flat). I alongwith my wife had repeatedly requested them to do the necessary repairing work including taking pipe outlets outside the flat(almost 80% of the flat owners had already did it long ago)but they did not pay any heed to it. Finally I had given a letter to the President/Secretary of the Association to sort out the problem.After inspection of my flat by the board members they were very sympathetic including Secretary/President and tried in many ways to sort out the problem but could not solve it till now.As per Association decision we also agreed to pay 50% of the cost but still the Upper Flat owner is not giving entry to their flat for undertaking the repai