How Do I update my phone number and zip code

How do I update my cell phone number  and zip code?  I had to open a new "On Demand" wifi  account, because of some weird ID glitch in the system. I could not log in. 

Today , Xfinity took my On Demand payment just fine, I got an email verification. And a "thanks for your payment " on my account here.  

HOWEVER , I understand that I need to have the "prepaid Comcast" division simply recognize my NEW phone number  in the "On Demand " database. The new phone number is on my payment info screen , as is my zip code, which I need to make sure is updated as well, so It matches my phone number.

I don't have an "account number" , that is not viewable on my account page or even on my bill statement . 

so I can.... 1. Order a modem , And 2. Set up my system as a "prepaid" after December 17, 2020.   

My "On Demand " service will expire on December 11, 2020.   I want to order the modem NOW to avoid the Xmas rush thanks.