If I understand you correctly, you can answer an incoming call on your watch but you can’t hear the caller’s voice.
Check the watch speaker is working. The easy way to do this is to use Siri and ask a question, you should get a text and spoken response. Does Mickey Mouse speak the time when you tap him?
Check the the audio level is not set too low. While in a voice call (phone a friend for testing) turn the Digital Crown to adjust speaker volume.
Can your caller hear your voice if you make a call from the watch?
You say you tried a reset. There are 3 possible reset methods. 1. Simple power off to restart. 2. Hard reset by holding both buttons until the watch reboots and shows the Apple logo. 3. Unpair the watch from the phone, then re-pair and setup again.