Presume you tried this, @Merisusa7
What happens when you try to access your voicemail from another phone:
@Merisusa7 - was voicemail working previously?
If not due to an update, try performing a Reset of your device's Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, VPN and APN settings, and connected Bluetooth devices that you've used before.
To Reset Network Settings, begin by opening the Settings app. Next, tap General -> Transfer or Reset iPhone -> Reset -> Reset Network Settings. and enter your passcode.
Your iPhone will reset network settings and restart itself.