Hi @Anonymous there seems to be s solution in this thread
Hi @Anonymous It was the same issue on this thread and problem solved
Also scroll down on this article. Plenty of tips given there https://www.imobie.com/support/how-to-fix-voicemail-after-updating-ios-10.htm
*The Game Is On*
Thanks for raising this to us last night and this morning. We're currently investigating the cause of this, but in the meantime what we have seen to work is sending a message saying "STATE" to 9011. This will reset the mailbox, but won't delete any of your messages.
If that doesn't work for you, please let us know.