So I used to live with my mother. She was the primary user. She made me a secondary user. We cancelled with Xfinity and she moved to another internet provider. I moved out and wanted to try Xfinity. When I just registered for the internet plus plan, I used the same email I used to sign up as a secondary user. How do I become a primary user for my own account when I was originally a secondary user?
When you open a new account, Comcast assigns a new Primary user ID for it. You can find what it is with the UserID Lookup Tool at https://idm.xfinity.com/myaccount/lookup. After you enter the requested information, the page will tell you the UserIDs on your account and indicate which one is Primary.
If your existing email address didn't transfer to your new account, Comcast Security Assurance might be able to help you. Give them a call at 1-888-565-4329 (from http://constantguard.comcast.net/help/report-abuse/). Note that this is NOT one of the general customer service numbers. The first-line reps there are sometimes not very helpful. If so, be persistent, and keep at them until you get a satisfactory answer.
Once your old address is transferred, you can use My Account / Users to make it Primary.