@Jelboy: Please can you take a look at the steps in the link below, to see if you're able to remove the voicemail notification.
https://www.samsung.com/uk/support/mobile-devices/how-to-remove-voicemail-notifications/
I also recommend pressing the Volume Down and Power buttons together for around 10 seconds until the phone restarts. Don't worry, this will simply refresh the software, and won't affect your personal data or settings.
