Non-Return Fee on Gateway Internet Wireless

You're probably going to need to go up the support chain in T-Mobile (though that may be hard). The original authorized return was most likely tied to the serial number of the first gateway, the one you didn't return. If the receiving department at T-Mobile entered the serial number of the one you actually returned, it wouldn't have shown up in the system as an authorized return. You're going to have to go beyond the first line support to get someone who can track this down. Having done equipment returns with three different cell companies, my returns were always tied to specific units. ¡Buena suerte!