Cannot delete mobile number from secondary account--lost 2FA from main account

I have the same issue described in this post: https://forums.xfinity.com/conversations/signin-and-account-management/cannot-delete-mobile-number-from-secondary-accountlost-2fa-from-main-account/63ebe84e65f3ed11c94eb405

I have my mobile number seemingly permanently associated with a secondary account and 2FA isn't enabled for that secondary account. I can't enable 2FA for my primary because my mobile phone number is "already in use by another Xfinity account". How do I delete my mobile # from that secondary account so I can associate it with the primary account. I actually don't need the secondary account at all so I'd be fine with deleting it if that's the easiest way to deal with this (as long as the mobile # association also gets deleted).