How long does a phone number sit in cold storage?

Long story short, when my grandma got a new phone, she changed her phone number but failed to update any information and is now locked out of her media (mainly her email) because her 2SV's are being sent to a dead phone number. We've tried calling ATNT but they said it's been 2 months since the phone number was disconnected and the account was closed (even though I swear it's only been a few weeks (because there were still calls being made mid Aug from the phone number. So how has it been more than 2 months already? >_<