iPhone voicemail issue

When someone leaves a voicemail on my iPhone 11, I can see that I have received a call because the "recents" icon at the bottom of the screen indicates a new call. But the nearby voicemail display does not show that the caller has left a message. A few hours later, typically when I am using the phone for another call, the voicemail indicator will light up and I will then be able to access the missing voicemail. But it is very frustrating not to be able to access the voicemail in a timely fashion. Any suggestions would be most appreciated.