Hi and welcome to the forums!
With the information you have given I have to assume that you have a defective device. There is no reason, no setting that would make it impossible for both you and your caller to be unable to hear each other.
You can try going into speaker phone mode during the call to see if that works as it uses the external speaker instead of the ear piece. See if you can at least hear your caller, and if perhaps they can hear you. If it works there and not on a standard call, you indeed have a defective ear piece and possible mouth piece as well.
I hope this helps!