Voicemail icon that is not Visual Voicemail

[Android Central Question]

I have an S8 and was happily using the visual voicemail. All of a sudden I have another voicemail app that for some reason seems to pick up some of my voicemails. I believe it's an AT&T app. I can't get rid of it. I can't locate it on my phone and the icon will not disappear. I'm at my wits end in trying to get rid of this icon and then how do I revert back to visual voicemail?

 

[Rukbat]

Which is the other voicemail app? If your carrier is AT&T, you probably have AT&T as your voicemail (the carrier maintains the voicemail server) so, unless you're forwarding a Google Voice number to your phone, and have Visual Voicemail set on that, what could it be other than AT&T?