Fixed it

I just typed all this out in a rage induced vent and the site crashed... I didn't even know websites could crash on a static page but... OK xfinity. 

Here's the fix

https://www.xfinity.com/support/articles/switching-between-multiple-accounts

Go there. Click the link to sign in. It'll take you to the accounts page. Top right icon. Open and click switch accounts. Then go back and unlink it.