After Jan's identity was stolen, the identity thief registered her account and added a fraud alert with the three credit bureaus.  The phone number on each account was not Jan's but that of the identity thief. Jan soon realized that her identity was stolen and contacted the three credit bureaus to freeze her credit.  When Jan called the credit bureaus she was required to send proof of ID by mail in order to update the alert with her number. 

Weeks later the thief changed it back to yet another phone number. But that's not all. The thief set up online accounts with the credit bureaus for managing the credit freeze. When Jan called the credit bureaus to activate a credit freeze, the imposter logged into the accounts they created and removed the credit freeze.  This allowed the thief to continue using Jan's identity to apply for loans, etc.  

Since the identity thief was able to add fraud alerts to Jan's credit reports, they were the ones getting the alert notices instead of Jan.  This allowed the thief to continue using Jan's identity without her getting the alerts from the credit bureaus.