@Emilye: Where is the notification currently visible? If it's showing in your Status Bar, please try heading to Settings > Notifications > Advanced settings > Show notification icons, then select None. If you switch back to your previous setting following this step, is the notification still visible? If so, try pressing the Volume Down and Power buttons together for around 10 seconds until the phone restarts. Don't worry, this won't affect your personal data or settings, but it will refresh the phone and should hopefully clear the unwanted notification for you. Let me know how you get on.