While the notifications cell phones provide when you receive a new voicemail are usually helpful, having the icon stick around even after you've checked your inbox and deleted or saved any messages can quickly become a nuisance. This may happen if you hang up without following the prompts to properly log out of your inbox, but network issues can also interrupt the signal that your service provider sends to remove the voicemail notification icon. In any case, the solution is simple.
Call your cell number from another phone. Let it go to voicemail and leave yourself a short message.
Access your voicemail account from your cell phone. Follow the prompts to listen to and delete the message.
Follow the prompts to navigate out of your inbox and leave the voicemail system. The icon will disappear.