Recovery of SBCGLOBAL Account (I8OO8I57.93O)with Lost Password, Phone Number and Security Questions

Question

I am a pc technician and I have a customer that has lost the password to his SBCGLOBAL account. He also no longer has the phone number for texting password reset codes. He cannot remember the answers to the security questions for the account (at least not correctly). For the verification list of subjects and e-mail address of sent e-mails from the account, I helped him recover e-mail subjects and addresses of emails sent to the account but not from the account as Microsoft requires for recovery. We requested a couple of the people to which e-mails were sent to also forward any emails sent from the account. My question is: Can Microsoft change the phone number for texting the reset code if he mails or emails to Microsoft proof of past ownership of the phone number with AT&T? He may be willing to pay some fee if necessary to get back into this e-mail account. Thanks.