Has anyone continued to have the issue after clearing the phone app cache? I have a Galaxy S6 with Sprint and after doing a factory reset have been plagued with the phantom new voicemail notification at least once a day, if not twice. Each time, I go into the Phone apps (I have 3 as well), clear data and cache, and it disappears for awhile only to return again. I do not have Google Voice as far as I know, I've never set one up, don't have an app with that name, etc.
This is incredibly irritating.