I have a Pixel 4, and have followed the directions to turn on Visual Voicemail. In the Phone app, when I go to Voicemail it says at the top "Activating visual voicemail. You might not receive voicemail notifications until visual voicemail is fully activated..." My VM account is set up, I have a pin, but the activation never finishes. I've let it sit for weeks, turned Visual VM off and then back on, but the same message shows and the setup never completes. Any thoughts?
I *just* had the same issue (Pixel 3XL). Wound up resolving it by going into settings and toggling between the on/off Visual Voicemail options. It finally activated and I'm receiving new messages. Good luck and hope that helps.