Friend can't be heard in voice chat.

I've had an Xbox One for a little while. My cousin just got one recently and we cannot figure out how to get voice chat to work properly. I cannot hear him at all. He can always hear me. We can both hear the dashboard and games fine in the headset. We both
have Turtle Beach DX12's. I normally work in tier 1 / tier 2 tech support for software and hardware, and I've been building and repairing computers for years. It's extremely rare for anything to get past me but this has been more frustrating than any PC issue
I've had to deal with in the past.

We've tested this out on 3 different computer monitors at his house, and a tv. We've used 2 different DX12 headsets at his house. Swapped out all cables (HDMI, 2.5mm cable from DX12 to 3.5mm adapter to controller), two different controllers with 3.5mm jacks,
reset the whole device, and even exchanged the Xbox for a new one. We've gone through all settings from top to bottom on both of our consoles. We've double checked the voice options in the gear icon when in a party. I've checked network stuff including router/NAT
settings in both households. This has been ongoing for a week now, and although I refuse to give up, it's becoming very tiresome.

The way we normally hook this up is (Monitor) headset 3.5mm to audio jack on monitor, usb power to headset, 2.5mm cable from headset inline volume box to adapter cable (3 band, and we both have the exact same cable), then adapter cable to controller 3.5mm.
On tv there is no headphone jack so we use audio composite red/white cable that came with headset into the tv, then 3.5mm green male on headset to 3.5mm green on other end of composite cable. We have updated firmware on all controllers.

I was thinking about the possibility of him being banned from voice, but he created a new hotmail account just for the xbox, and new xbox live account. His ID is Sfinkternator, so not sure if he would be banned simply from that but if he was I would assume
he'd be notified and it would be obvious that he's banned.

Open to any suggestions.

:)

 

Xbox one headset not working

So I haven't had much issues until now. My headset was working perfectly a few hours ago but now I am unable to chat to my friends in party or game chat. The headset isn't registering my voice. The mute button and volume buttons are both fully functional,
yet my voice can't be heard. Hard resetting and resyncing the controller to the console has made no difference.

 

Self Muted

Are you able to be heard in party chat or in voice messages?

 

I would say its a NAT issue due to one of my friends having the same problem, but you say you've checked that?

Have you tried switching from game chat to party chat? That is the only thing that works for my friend.