Incoming calls problem to voicemail

Check if call forwarding is enabled and turn it off if it is, ensure "Do Not Disturb" is disabled, verify that important contacts aren't blocked, reset network settings to fix any network-related issues, and contact your mobile carrier if the problem persists.

Here’s a new user tip from one of our most distinguished members which might also help:

VoiceMail is a carrier-specific feature - Apple Community