My Stereo Mix is not outputting audio.

The stereo on my headphones are not working. The only setting that actually puts out sound is when I select Hands-Free AG Audio, but it’s very fuzzy, low quality and sometimes the audio plays back with weird noises in the background. The Stereo Mix was much higher quality and clear, but it started to play audio really quietly, and then one day it just stopped completely. I’ve tried testing the audio for the stereo, but it seems like it’s completely broken. Does anyone know how to fix this? I have had these headphones for less than three weeks. help