I put the question to Telstra and was told the key is to ring the call centre and ask them to "submit a request for a service qualification test", if the cable is in your street and you believe you should be able to access it. Even if Telstra runs copper to your home, the cable access maps aren't updated after it's laid in your street so they don't acknowledge the existence of new dwellings.

http://www.smh.com.au/technology/gadgets-on-the-go/the-trick-which-might-get-you-off-flaky-dsl-onto-telstra-cable-broadband-20161222-gtgsj1.html