I have less of a question, and more of an answer:
Around a month ago I hit the "update system software" on my Samsung Galaxy S6, then my Google Voicemail stopped answering calls. Callers complained they received a standard message from Verizon that my Voicemail had not be setup yet. So, no one could leave a message.
I went into Google Voice & verified I had not changed any setting to the system. I uninstalled & reinstalled Google Voice App on my phone - and received a message that Verizon does not allow Google Voice as the default Voicemail. I thought this was strange because I have been using this app on my Verizon Samsung S6 for over 1 year so far.
After calling Verizon for help, and getting no where. I ventured into the google forums & found the SOLUTION.
I went to my Google Voice Account / Setting (gear in the top right corner) and clicked the "De-Activate Google voicemail on this phone", followed the prompts to do so. Then I clicked on "Activate Google voicemail on this phone". Voila - it worked!! So happy with myself I thought I would share. Here is the link for the Google Voice help site for complete instructions; just be sure to deactivate, before you activate. Turning it off, then turning it on fixed my problem!