No audio in Overwatch for Xbox One
This seems to be related to the Xbox One's standby mode. Putting the console on standby with Overwatch running often causes this issue.
Force quitting and restarting the game seems to fix the issue. You haven't messed up with any of the settings, don't worry - just a buggy game (I had that issue once on PC too).
Try to restart the game and then the console itself if the issue isn't fixed.