It is imperative that your lost or stolen card be reported immediately to AT&T. Please contact AT&T Customer Service by dialing 800 CALL-ATT (800 225-5288), prompts 3 and 4.

How do I report a lost or stolen AT&T Corporate Calling Card?
It is imperative that your lost or stolen card be reported immediately to AT&T. Please contact AT&T Customer Service by dialing 800 CALL-ATT (800 225-5288), prompts 3 and 4.