According to the Common Property Memorandum on the NSW Government website, internet and cable wiring within common property walls is the responsibility of the Owners Corporation, as is internet wiring serving more than one lot, regardless of whether it is contained within any lot or on common property.
But here’s the thing, they must have taken the exiting wiring out or disconnected it and have done so without permission, so if they’re saying it’s common property, then say fine, pay us for what you took out because that was common property too.
I would tell them to go whistle for their money or call it a quid pro quo for the damge they’ve done.
Too many contractors see strata schemes like the local council which can be ripped off with impunity, and they encourage their apartment owner customers to thisnk the same way. I wouldn’t give them a cent.