Request for a replacement AT&T TV wireless box

I have a silver motorola AT&T uverse box that displayed a red x on the TV screen and green and red blicking lights on the box. We tried to turn off and turn back on and reboot it by holding the power button down on the tower. We also tried to unplug from the wall and plug it back in. No change. AT&T says all the lines are working but not the box, second box went down. Three others are working.