Not receiving calls from a certain number but I get their voicemail.

There are a couple of reasons this could happen. You have done a great job of troubleshooting so far by checking for blocked numbers and verifying that Focus is turned off. If you have other Apple devices, verify that Focus mode is not enabled on those devices or, if you want to leave Focus mode enabled on those devices, you can toggle Share Across Devices off. Settings > Focus > Share Across Devices (Toggle Off).

If this doesn't work, you can try resetting your network settings. Of course, you would want to back up your phone. You would go to Settings > General > Transfer or Reset iPhone > Reset. Doing this will remove any of your currently saved Wi-Fi passwords, VPN settings, Bluetooth connections, and other network-related settings.

If you would like to save your passwords and WiFi settings, you can backup your iPhone to your computer using the steps shown here: https://support.apple.com/en-us/HT205220

I hope one of these steps helps with your issue.

They may have blocked your number accidentally. Even if you are blocked you will still receive VoiceMail. Hence you are neither receiving nor able to make calls.