Door entry system in flat not working (is it just my handset?)

Since moving to my flat earlier this year my door entry handset has never made a noise when someone presses buzzer, and have never had the ability to use the two way audio. I could only ever let someone in using the handset. However, now the ability to let someone in with my handset is also gone. Others in my block say their audio works, and they can let people in. Property factors want to change the whole system, but other owners (quite rightly) wont pay if its only mines that broken. Does it sound like its just afaulty handset or a fault of the whole system?