I would try wiping the cache partition but if that does not work, I would recommend contacting your carrier since voicemail is carrier controlled.
- Turn off the device.
- Press and hold the Volume Up key, then press and hold the Side key.
- When the green Android logo displays, release all keys ('Installing system update' will show for about 30 - 60 seconds before showing the Android system recovery menu options).
- Press the Volume down key several times to highlight wipe cache partition.
- Press Power key to select.
- Press the Volume down key to highlight yes, them and press the Power key to select.
- When the wipe cache partition is complete, Reboot system now is highlighted.
- Press the Power key to restart the device.