Per AT&T, they can't cancel an order that is preparing to ship. Only thing you can do is:
A) call carrier service (FedEx or UPS) and cancel the delivery once you have a tracking number/reject package at time of delivery or
B) accept it.
Been going through run around with AT&T since Saturday about this. They can't even cancel your service with an item marked "Preparing to Ship"...They are a joke, but signal wise, best in my area. As long as I don't have to deal with their customer service, I like them 🙂