Need help up grading paid in full device!

The day I started Xfinty Mobile with BYOD, I tried to add another line and got the message that based on credit I wasn't eligible for Xfinity services. Customer service told me that it was because of the phone, and then to wait 3 months and it would disappear. It never did. Fast forward a year and a half later, when I try to upgrade phone, add a new line, or purchase a device in full it says the same message. Customer care says I have upgrades available but they aren't sure why the system won't allow me to do so. One says to wait another 3 months, one says maybe my birth date was entered incorrectly. One says it has nothing to do with credit, but maybe my account isn't in good standing. Noone can give me a answer as to why I keep getting the error and why it can't be overwritten. I need a new device.