False voicemail badge on iPhone 13 after iOS 26.2 update

I have just upgraded from iOS 18.x to iOS 26.2 on my iPhone 13.

I now have a voicemail indication ("badge") that a new message has been received even though there isn't one. I've followed the steps on many (older) posts to try to remedy this, without success, and spent much time today on the phone with T-Mobile to try to fix it. They believe that it's an iOS problem.

Does anyone have some suggestions for how to remove the false red dot?