Ambushed: Can anyone please post screenshots?
I can do it when I get home this evening, but won't be until about 7pm.
If you are getting sync and PPP Auth, then that suggests your connection is fine, and it's the modem that is screwy.
If you followed the instructions above (removing all existing connections, adding only a new WAN one, and leaving all settings as default except putting something in the username/password slot) - which seem to work for everyone else including me - then I'd say it might be worth re-trying them over again from a factory reset, just in case you mis-read it the first time and accidentally changed something without realising.
The other explanation is that your modem is faulty.
FYI TimA - I used the NF4V without a public IP and it works fine, so I don't think it is CGNAT