They mean someone else got your password and used it. Kids love to do things like that. You should have gotten email notifications of the orders however. They wouldn't know it was hacked anymore than you would until someone started making changes.
A012, I'm sorry to hear we have lost you as a customer. If you did not purchase the phones I recommend sending them back and reaching out to our security assurance team so they can investigate. We take these matters very seriously. Please go to www.xfinity.com/fraudclaimform to submit a claim or call the Customer Security Assurance ID Theft team at 844-335-8719 as soon as possible.
Zerokool316, did they tell you what damage was reported on the returned phone?