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I understand from your post that you can no longer hear callers and callers cannot hear you during calls on your Apple Watch. In a situation like this, make sure that the call volume is turned up and that mute it not enabled. The Apple Watch User Guide has additional information on adjusting the volume you may find helpful:
Answer phone calls - Apple Watch User Guide
Adjust call volume. To adjust the speaker volume when talking on Apple Watch, turn the Digital Crown or tap the volume symbols on the screen. Tap the Mute button to mute your end of the call (if you’re listening on a conference call, for example).