Unable to change the phone number associated with my account

Hello, 

*I am currently using a Samsung S10e - OS Android 12*

I just now logged into my Xfinity account to see how best I can help correct the major issues I'm currently having with my Xfinity Mobile and Xfinity Essentials account.

  While reviewing my account, I saw that an old number I no longer have access to was still registered as the number associated with my account. I tried to change it but upon submitting the new number, the message "Error Modal" appeared under the submit button and I could do nothing else...

The Xfi app shows the correct number, but the Xfinity website does not. Can someone please explain why I can not change my number on the website, why my numbers are different for each platform, and which number is the one that's actually associated with my account?