Hey,
I had the exact same issues when using my own router.
You need to phone them and ask them to clear the MAC Addresses for IPv4 and IPv6 from their cache due to its got stuck and then you need to have your router reconnect and that should be it, in fact I was on the phone and the Tech Guy knew exactly what the issue was and they cleared it while on the phone.
What they will do is drop your current router's connection on both IPv4 and IPv6 and then your router should then just connect up.
For IPv6 I just have my router request for a Prefix.
Here is a
BQM via IPv6, its not that pretty but its working fine here.
Also have you tried connecting your PC to their Modem instead of using any router, how did that work ?
Either way I think its due to sticky / stuck MAC's that needs to be cleared.
Paul