unable to connect to one friend in party chat

Now from what i've researched this is nothing new dating back to 2012 but my friend and i have been talking in party chats almost daily for 4 years but suddenly out of the blue 2 weeks ago we can not connect to each other at all it doesn't even try on the
odd occasion it'll let us join for about 5-20 seconds then we disconnect and then not allow us to rejoin so for 2 weeks now we've been calling ISP's checking our internet connections, contacting xbox online support trying all their suggested trouble shooting
and other ways to resolve this issue and it still wasn't resolved all they could say was that we had stumped them. We then started to call xbox support for any new ways and tried the ones they suggested and still not working we've done port forwarding, DMZ,
UPnP everything possible even looking online for anyone else who has had this issue and trying their ideas but still nothing.

The thing that makes this so strange is we able to join other peoples party/private chat no problems and i can join his brother in a party/private chat and they use same modem/router also if we try to join each others games it will kick the other person
out of the game. We can also send and receive text and voice messages

Neither of us has blocked communication ever and neither of us has ever had a ban/suspension from xbox.

This is getting ridiculous and way beyond a joke what are me and my friend paying gold membership for this issue should not still be going on for 2 weeks.

If anyone knows how to fix this please for the love of god do tell me before i get a sledge hammer to my xbox

:)

 

Game/Party chat fail

My xbox is is the same situation. earlier today and yesterday evening I was unable to connect with friends via party. In game chat seems to function alright.

 

This same "error" has been happening since xbox one launch.

Really you are able to connect to your friends list? and you have never had a problem with the party chat? i think that's highly unlikely since everyone for the past 2 days has been unable to connect and play with their friends.

 

So, the general cause of this will be your NAT type. If it's either strict or moderate you'll have issues, however if yours is open then the problem is on their network. To find your NAT and fix this you can follow the steps in this link, or direct your
friends here if your NAT is open -- support.xbox.com/.../nat-error-solution

 

Thanks ThisFuppingKid but we've both checked our NAT and we're both open we wish it was as simple as that lol