I understand you are experiencing issues with your A40. Here are a few steps you can take to attempt to remedy the issues.
Make sure that the mute button on the front of the MixAmp M80 is not enabled (The mute button should not be illuminated).
Hard reset your Xbox One by holding down the power button until it completely powers off. You should be able to hear it click or shut down full.
Try using the provided inline cable and the headset on a smartphone and see if you can be heard during a phone call.
Make sure your controller has an unblocked line of sight with the console. Even a glass window can cause interference.
If these steps did not alleviate the issues you were experiencing, please go to the link below and submit a case. Let your agent know all the steps you tried and the outcome of your troubleshooting. It will help speed the resolution of your case!
Support Channel: https://www.astrogaming.com/contact/