Unable to hear other people talking on COD with turtle beach px21?

I have bought the PX21 last month and it was been working fine until recently. The game sounds and the mic works perfectly apart from the fact that you're unable to hear the people you are playing with talk. I have turned the chat volume up and the options on COD are perfectly fine, at times you can slightly hear the people talk but other than that it's very distant and discreet, please help?