This is from the manual:-
Bluetooth usage: 1. Making phone calls: Be sure the earphone connected with your mobile phone, and then you can make phone calls. When making calls, there is only one side earphone working, and there’s incoming call, it would broadcast calling numbers. You answer the call by slightly press the power button one time and refuse to answer by quick press the power button 2 times. When the earphones are in music mode, you dial your latest number by quick press the power button 2 times (redial the latest number).
Are you following this routine? There may be a compatibility problem, with your phone if you are following these steps.