Voice mail notifications is an issue on the Verizon side, not your Blackberry, more than likely. Call customer service and see if they can get it going for you. It's just probably something simple they can do to get you up and running again with notifications. Let us know here in the forums if you do not get it working.
I have a plain old cell phone and have experienced the same problems. I will get a voice mail notice, and it will be from a voice mail left weeks ago. I've called customer service, and they explained that the problem is that you have to update your phone's links to whatever new towers have gone up. Here is what you do:
when a voice starts talking, press #2
it will then do its thing. When its finished, call your cell phone and leave a voice mail to see if you get notice of the voicemail. If you don't, then I don't know what you do next, other than call customer service.