Have you checked your call screen? Is audio being redirected to headphones or BT? Does it work OK if you switch to speakerphone? Is your call volume set to an appropriate level (had to ask)?
I'd suspect the carrier. Bring the phone into them, have them call you and hear it themselves. They have people they can call that you can't. (If you can hear an outgoing call, it's not the audio, the earpiece or the volume.)