My son had this problem, but he was trying to call back home to family while on TDY. His was caused because they all had the same phone number and email set for FaceTime. Once he changed the iPad to a different email address and NOT the phone number, it worked. But this was inner family communication. FaceTime is based on your iTunes account. Try turning off or deselecting the phone number and use a totally different email in setting under FaceTime, especially if you have an iPhone on that, too!