my friends hear themselves through my headset

i bought my headset (NOS H-800 wireless) just a month ago after my old pair broke and since i started using them, i've had trouble with people hearing my sound through my microphone. if i'm playing a game, watching a video or just talking in voice chat, they will hear my sound replayed through my microphone. i'm unsure about how to fix it. i'll buy a new headset if necessary but i want to be sure that the problem can't be resolved first.