Voicemail problems

Visual voicemail not working. When I try to save a custom greeting I get this error message. My voice mails are not being transferred to my phone, and I am also not getting any notification that I have a voicemail. I have a 256 GB iPhone XS . I have Verizon cell service, but this issue in not specific to Verizon.

Googled it, tried the suggestions that were online-none worked.

Spoke to Verizon and Apple spent several hours but they could not correct the problem. They told me to wait 3 days and maybe the phone would fix itself. It didn’t!

Called Apple support-on the phone with them-still not fixed! They were to call me back the next day with a more experienced support tech-still waiting. Visual voicemail remains inoperable after 4 days of investigating every possible solution. Needless to say, frustrated that this simple issue can’t be corrected! Any suggestions?