"This email address is already associated with an Xfinity account"

When I was getting my initial service set up, Xfinity inadvertantly used the wrong address and created an account now linked with my personal email address. That's been fixed and I now have a proper account with the correct address. However, the defunct account still exists — linked to my personal email. I'd like it deleted so I can link my email to the real account. I can't remember login info for the now-defunct account. Does someone know how this can be done?