MY mic has suddenly stopped working. I can hear people but they cannot hear me. I also can't send voice messages as it just records nothing. Iv'e checked im on the right chat channel for the game and my privacy setting but nothing
Is your Xbox360 still under warranty- If so then phone MS Support and they'll send you out a new one. They don't even ask for your old/broken one back. Your warranty covers all components of the Xbox360 not just the console.
One of my mics had a similar fault, you could hear but not be heard (thought folk were just ignoring me a usual ).
Explain that you've tried it on a m8's console and their mic in yours etc. and the fault is definitely with the headset. A new one is sent out within 3-5 days.