There’s a strange little quirk in the law relating to the installation of NBN and other communications services.
The owners corp can’t refuse to let the installers have access but they can set the times and under what circumstances they have access, as well as put limits on their work and charge them fees for electricity etc.
However, some NBN installers – especially those on a tight schedule to do a number of buildings in a certain limited time – think they can just turn up and if there’s no one there to let them in, they can break in.
They can’t without a court order – that’s trespass and property damage.
Get in touch with the installer and demand they repair the door and replace the lock or you will report them for criminal damage.