I have a similar problem... I get that visual voicemail message and the red notification dot on my iphone too now.
I can make it go away by switching on my mobile data - 4G. Everything works hunky dory when I do that. voicemails and everything works great with no error message...
When I turn my mobile data/4G off, then the red dot and the message comes back again. Visual voicemails are currently unavailable it says...
Now, I don't think there's anything wrong there. I think visual voicemail is supposed to only work when you have 4G or 3G turned on....
I just don't want the silly notification message there when 4G is turned off. Is it possible to make it go away, or is this little red dot part of iOS 9?
I get the feeling that it could actually be a part of iOS 9 ... since my Dad also now receives this little error message when the mobile data network is switched off.