Back online with a reliable connection after a lot of messing around with connecting Optus ADSL2+ last week.
Looks like I got a dodgy modem from Optus, will get a different model tomorrow to test. In the meantime I’m still running the old ADSL1 modem which works fine but not up to full speed capacity yet.
I’m not expecting much compensation from Optus for the time they lost me, but will press for all I can get and see what they say.. They have all the power unfortunately.