Slingshot GigaBit line + Fritz!Box + XBox Live = Issue

I am sure the appropriate people will move this to a different category if i am incorrect here.

Location: Hastings, Hawkes Bay, NZ

ISP: Slingshot

Router/Modem: Fritz!Box 7490

Issue: Unable to connect to XBox Live party chat function

On Tuesday of this week i had upgraded my Slingshot fibre plan to a GigaBit down, and with this i received a new modem (or router?) from the ISP, this unit being a Fritz!Box 7490.

Before this i had a lower tier (650/750Mb/s down maybe) with the standard, white modem provided by slingshot when you upgraded to fibre (unsure of the unit name/model, as it was packaged up and posted back)

And also with the standard "Optical Network Terminal" (gateway?) which is installed into your house/wall when you first get fibre connected up.

Now i arrive home on Tuesday evening, and my wife had gone to the trouble of setting up the new modem before i had got home, which is a pretty simple task, un-plugging and re-plugging the various Ethernet cables/power etc. Everything is working fine, TV's streaming, Phones/Tablets/Desktops/Wifi all is fine and running as fast as anything. Untill i try to log into XBox Live and join a party/chat which then throws me up an error "cannot connect to Teredo IP". So this of course takes me to uncle Google and the standard trouble shooting takes place. After the normal connection checks, resets, power downs and such are undertaken, still no luck.

I get to a point where the Xbox troubleshooting suggests i contact my ISP regarding some port forwarding suggestions i need to adjust on my modem end, So i contact Slingshot and mention my situation, which in reply to my query i am told because my internet connection is working, TV's/Wifi/Desktop's are all connected and working fine, it is not a problem of Slingshots and that i must contact my Supplier (Microsoft) to resolve this issue. Regardless of 24 hours earlier, on my previous modem/package it had been working fine for the past year. Yet when i upgraded my plan, and installed the new modem they had sent me this problem occurred.

So i make my way to the XBox support, and once again starting from scratch, we together go through the whole trouble shooting steps i had previously already done. Yet again to no avail. So we eventually get to the point of asking some networking terms i am not knowledgeable with, asking that i may need to "open my gateway bridgemode"

Make sure Parimeter Network (DMZ) is turned off

and Allow Teredo tunnelling / Allow IPV6 tunnelling is all Enabled

At this stage i get Slingshot back on the phone, the time was 9.56pm and unfortunately for me Tech support closed at 10pm. At this stage i had had enough, and kindly said thanks to both parties involved with my enquiries, and proceeded to call it a night.

Now unfortunately by the time i knock off work, do the normal afterwork stuff (kids, food, everything) its pretty late to be sitting on phones with someone in the states, and my extremely helpful ISP support trying to fix a problem, just because i wanted that little bit more bandwidth.

Why not revert back to the plan i had before? it already worked.

- Because being a user of computers, and the internet since the early 1990's, you do not go backwards when it comes to bandwidth.

So my question to anyone who may have any idea regarding this issue, if you could point me in the right direction with regards to settings/port forwarding/teredo tunneling etc i would greatly appreciate it.

I am not a networker, that was never my strong point. All i ask for is some help

Regards

Hamish