Shared apartment wall has been damaged by neighbour's pipe

[athene_niu]

My duplex was ground floor and first floor, our yard shares the same wall as the other apartments. But recently I've noticed something wrong with a pipe from their apartment, they have dirty water flushing down to our yard all the time, and it's getting worse day by day.
I've send email to management company, they said they notified the owner of the apartment. But after that, nothing happened.

In this case , what should I do ?

 

[elcato]

Can you put a note under the door of the apartment or contact them directly ? Even if it's let out I'm pretty sure the tenants will at least try and do something about it. Chances are no-one actually knows.