What is the address of AT&T Corprate office?

My most recent bill from att is over $5000. This is clearly a mistake. When I triid to tell them they wouldnt hear me out. I must have wasted over 2 hours talking to many different people and supervisors. I finally called the clark howard help desk and they said i need to write a letter to their corprate office. I coulndt find this information on thier website. Can anyone please help?