Apologies, lurked a few years ago, but first post here.
TLDR: You can't use your own router or their router's dashboard portal if you add their telephone (VOIP) offering.
To put into context, the router I had was working well (and I had portal access) for over 6 months with them, only until recently when I added their VOIP offering did their technicians decide to lock the router portal.
Something as simple as changing the wifi name or password or enabling guest-wifi when you have guests over is apparently something that is beyond Nova.
I believe they are relatively new to the broadband internet space, so I thought I'd let you guys know.
In saying that, I appreciated their call handlers being quite patient as I clarified several things. (they don't allow customers to speak directly with their technicians - so it was a process of relaying between them back-and-forth)
PS: Yes I tried resetting the router - seems they flashed the firmware from away the default admin-admin login.
And no, you can't use your own router until you cancel their VOIP addon.