Oh I used to have those.
You know the mic I/O switch and volume wheel on your headset?
Basically that thing apparently breaks or screws you over quite easily because of the chip managing your sound or some tech shit breaking for the left side of your headset.
Have you tried tampering with the volume wheel just slightly and perhaps the mic button to see if it works. As in slightly nudge it in one direction or the other.
It worked for a while for me but eventually that stopped working too and I gave up on the headset.
You could always complain to the manufacturer I guess but I just threw them away after that and made it a life lesson to not buy SteelSeries devices again.
(I also had a mouse from them where the scroll wheel stopped working properly as well, quite some time before my headset broke though.)