How to Fix your Oneplus One Mic Issue [ Guide ]:
1. First go to your Phone Dialer and open settings. If you are using third party app then go to app drawer and open phone dialer from there.
3. In settings menu tap on other settings > Open TTY Mode.
4. Disable the Open TTY Mode by tapping on TTY Off.
All Done ! Now plugin your headset and Your Oneplus One MIC will work while talking.
How to Fix your Oneplus One Mic Issue [ OS Oxygen ]:
1. Open Dialer and the tap on 3 dots, select Settings.
2. Now select Call Settings for the list.
3. Tap on TTY Mode.
4. Tap on TTY OFF.