Voicemail has suddenly gone away somewhere...but where?

Hi there - when calling my iPhone 8+/iOS 16.1.2 (which is about 2 years old), a friend told me there was no greeting on my phone and they were unable to leave a voicemail.

I called my voicemail - the greeting was there (although now quite muffled - it was clear when I first recorded it). I then recorded a new greeting - there was no option given to 'save' it but when I called my voicemail again the new message was there - but when someone called, again there was no greeting and no way to leave a voicemail.

I have no idea how this happened - I've never had any problems with it in the past.

If someone could help me out, that would be great - especially if there was a way to do so without a full reset. Thanks in advance.