Landline voicemail

A few days ago, my landline phone's voicemail stopped working.  I went to set it up and it said there is not voice mailbox for my number. All answers on forums or searches state to use the old app, Xfinity my account. However, I have the new app as the chat line told me to use. Neither have been able to help me. I've searched on the computer too and I get the basic set up to reset my router, which I do not want to do or to do the basic set up which when I dial *99 it won't allow it. Feeling frustrated!!