Be Right Back, Uninstalling

I've been trying to play games on my Wii U and Nintendo 3DS for a while now, ever since my ISP installed a Technicolor TG789vn v3 I haven't been able to play online.

Both Nintendo consoles can connect to the internet, browse, open and buy things from the eShop and even download DLC, but when it tries to connect to a matchmaking server such as Mario Kart 8's or Smash's it throws an error.

I tried to forward the recomended ports (Nintendo says to open all of them), but the router has a weird system where I have to assign a group of ports to a profile and then link that profile to a device. The same ports can't be assigned twice to different decives (and for some reason, port 80 can't be assigned to any). Anyway, I tried it, it didn't work.

I tried to put the Wii U in the DMZ, which worked perfectly, but it won't let me add another device and if I try to put the 3DS in there I will have a really unstable connection, losing the signal every 5 seconds. (I'm less than 5 feet from the router).

I have no idea what else to try, got an idea what else could it be?

Nintendo devices don't play nice on channel 6 for some WiFi antennas.  Set your channel to 1 or whatever the higher may be (usually 11 but I've seen higher).

Also, some wireless devices have problems with routers that are both 2.4 GHz,  and  5 GHz. Typically turning off the 5 fixes these devices (common with first generation Google chromecasts).

Sent from my wireless communicator.

Please note that you can forward an external port to only one host at a time. DMZ is treated as automatically forwarding all unused ports to the IP in the DMZ. I haven't seen a router that allows multiple systems in the DMZ.

Do you have a second router/gateway/wifi-anything inline after your ISP's Technicolour TG789 gateway? If so, it's possible that you are doubled NATing your devices, which would explain your issues.

No, the only moden/router I have at home is the Technicolor :/