Voicemail Greeting

I have an iPhone 8 (Verizon) and cannot seem to get the personalized voicemail greeting to save. Each time it is saved, it reverts back to the default setting and when I receive calls, it says that the voicemail is not set up. I've tried saving both on and off wifi, I've reset my network settings and I've restarted the phone. Can anyone offer suggestions on how to resolve this?