UPDATE No. 2 - 3 days later and no modem has been delivered. A 'case manager' called me yesterday to tell me he'd spoken to my wife 24 hours ealier and understood the situation, and just wanted to clarify it with me. I'm not sure why that had to wait 24 hours and why he coudln't act on what she'd said to him, given that she's authorised to make changes to the account etc. I told him I was no longer interested in having a Telstra NBN service and he said that 'was ok'.
The complaints manager never got back to me. Last thing she said was that she'd chase up 'dispatch' and get back to me 'right away'.