My previously totally reliable and performant UFB connection stopped working suddenly about a week ago.

Since then I've been on the phone with my ISP (ICONZ) daily and they've tried to bounce it around to Enable (I'm in Christchurch) and 2Degrees, declaring a couple of times that it is "fixed" but to no avail. 

As far as I can tell the router can see a PPP server, the log suggests it makes a connection but the password/username auth fails. ICONZ says they can't even see the failed attempts.

Unfortunately, my mental model of how UFB works is not really solid enough to know what could be going on. I assume that somewhere I should be "magically" pointed to ICONZ and that their PPP server would process my authentication request? Or does it not work that way? My ISP says that when they configure a router with my credentials it works for them. It seems to me that I'm being pointed to the wrong PPP server, in which case somebody has been getting failed auth attempts every 20 seconds for the last week!

Does anybody have any suggestions for things I could try? I've had the same problem with two different routers, replaced all the cables and yes - cycled the power on everything that has a power switch including the ONT. Been reliant on my phone/4G and it's getting expensive...

Thanks,

Quentin