Calls still going straight to voicemail.

Despite following the extensive list of 'checks' on one of the community threads to ensure calls do not go straight to voicemail, they are still doing this. Another important call from the hospital missed because it went straight to voicemail!

On another discussion on this community site there are a list of things to check, including Unknown callers, Do Not Disturb etc etc. I have checked all of these, and there is no reason why I am missing calls.

Can Apple look at a fix for this 'bug'? I can see from this community and from Google searches this is a common issue. I don't want to leave Apple, but I really do need a phone that works as a phone as I am dealing with the hospital for the rest of my life and can't go on missing important calls.