My Caller ID shows someone else's name when I call a landline.

I have owned the same mobile phone number for over 20 years now. About 2 years ago I cut AT&T loose for Xfinity Mobile. All was great until a few months ago all of a sudden I started showing up as someone else when I called a landline. I have spent several hours on the phone with Xfinity and they all assured me that it would be fixed within 72 hours...NOTHING! This is a serious issues as I use this phone for business and people do not answer based on the unknown caller id. The bizarre thing is that I have had this number at least 20 years! I'm about to dump Xfinity and find something that works. Any suggestions?