Your headset can be used as stereo headphones or a wireless microphone for a bluetooth enabled device like a cell phone or a computer. When you plug the headphones into a device with the 3.5mm jack the headset automatically turns into stereo headphones and disables the microphone(headphone mode). It sounds like whatever device your headset is connected to via bluetooth is using the wireless microphone protocol where sound only comes through the one speaker and the microphone is on(microphone mode). The bluetooth protocol settings of your device may have been changed accidentally. You will need to go into the bluettoth settings of your device you are using with your headset and change the protocol. If it is a cell phone you will need to go into the bluetooth settings in the settings menu. If it is a computer your can adjust the bluetooth settings in the control panel.
You can download the pdf file of your instruction manual for your headset here
I hope this was helpful and let me know if you have any other questions. Thanks for using FixYa