keep pushing and pushing them, dont give up, theyll get bored and do something.
As an aside I had on the 5th floor water backing up into my sink once, reckon all the other people in the building threw their cooking oil down the drains blocking or restricting the main pipe which all floors feed into. Office said it wasnt their problem, told em to go to the access point and rod the main pipe.They did nowt until we started to push them however I couldnt wait any longer, in the end I rerouted the sink waste into a washing machine wastepipe as I have the full plans for the building and the two arent linked and as such no one can chuck cooking fat into that separate pipe. Both are grey water so its no problem . Id rather sort out problems myself but as yours is an exterior wall its THEIR problem, get a lawyer to send them a letter, kick up a fuss otherwise theyll just keep smiling away forever and a day