My wife is still using her AOL email from 1999. I tried to add her as a user on our xfinity account a few months ago so she can have a comcast email. When I did, it wouldn't work and kept looping back to an error message. I gave up. She is having more issues with AOL blocking and trashing emails before she sees them. Now when I try to add her on xfinity it says there is already a user with her phone number. But she is not listed as a user.
When you set up your own account, did you use the phone number in question? If so, that would cause what you are describing.