Can't get rid of voicemail notification!?

[GIBXO]

How in the blue hell do I get rid of this voicemail notification?. I haven't even got any voicemail to listen too. (O2 UK) And clearing the app data/cache under apps/phone isn't working either!?

[Mo BETTA]

I found a fix. Looks like T-Mobile is moving to a native Visual Voicemail app within the Phone app. Open Phone app > 3-dot Menu > Visual Voicemail. After setting up Visual Voicemail, you should have another tab at the bottom of the phone app near Recent and Contacts (can take up to 2hrs to appear according to T-Mobile support).

Note: Allow notifications is no longer greyed out on Voicemail category after setting up this version of Visual voicemail.