The GV website you explain what you need to do. I have put into my contact list a contact that I created "Google Voice Reactivate" which has the *718xxxxxxxxx number to call to reactivate my service.
Every once in a while, including when I was using my Blackberry, prior to the Maxx, a call would come in and slip into the Verizon Voice mail service. I was always able to quickly identify this situation by the different notification icon that came up. In those rare instances, I would dial the *73 to disable my voice mail. I have always left "1" as the stock voice mail shortcut and "9" as my Google vm shortcut. I would then just use "1" to retrieve and then delete the vm that went to the Verizon. Once I was done with that, all that I needed to do was to call my Google Voice Reactivate number from my address book. Might have to do it twice due to the phone company requirements, I'm not sure because I haven't had to do this recently, but it does work. Having set it up this way, I never need to do anything on the GVM website. Not including listening to the wayward vm, the whole process should be done in less than 60 seconds.
I have had to do this maybe once so far since switching to the Maxx in June, and it works exactly the same way.
You might want to check the GVM website to ensure that you haven't deleted your phone or made so other inadvertent changes.