Wait are you on the old voice setting. There is a report in forum a few about it “hearing” but not responding. I had that issue a week or so ago.
This is that rabbit hole 
OpenAI Developer Forum — Voice chat listens but doesn’t respond - ChatGPT - OpenAI Developer Forum
OpenAI Developer Forum — Voice mode not working for custom GPTs - Bugs - OpenAI Developer Forum
OpenAI Developer Forum — GPT voice mode is not working - ChatGPT - OpenAI Developer Forum
OpenAI Developer Forum — Help with chat gpt not hearing my voice - API - OpenAI Developer Forum