I want to get rid of my 90 yr old mother’s voice messaging-help

This is really frustrating, I have spent WAY too much time trying to either extend the rings to maximum so her home “visual” answering machine picks up prior to her Comcast / Xfinity-She does not use the voicemail and has not for years.  How do we ( she and I) cancel this off of her acct?  It is making problems for her receiving calls.  Please help us.  I have done my best to figure this out but there is no option on the Xfinity site.  All suggestions via forum, do not work because the options stated are not available.

Thank you

Sarah