Visual Voicemail not working on iPhone XR

Make sure you iPhone is updated to latest iOS version. Then please reset your network settings.

Reset your network settings

If you're using iOS or iPadOS 15 or later, tap Settings > General > Transfer or Reset [Device] > Reset > Reset Network Settings.

If you're using iOS or iPadOS 14 or earlier, tap Settings > General > Reset > Reset Network Settings.

This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.

And you’re on iOS 18.2? You will need to check with your carrier to confirm they are still supporting the service. Not all carriers support it.