Since you originally wanted chat rather than a phone call, I would not immediately create another case, because that could create duplicate support requests.
If the callback comes and you prefer written communication, you can tell the agent that you originally selected ‘Chat with a support agent in your web browser’ because you need written communication. The system unexpectedly converted this into a callback request. Could he please switch this case to web chat or provide a chat-based follow-up option?
Also, don't post the phone number publicly.