here is their customer support number 1-800-T-MOBILE and here is their return policy Device Return and Cancellation Policy for T-Mobile.com, 1-877-387-4324 and 1-800-T- MOBILE sales and activations only:
You may cancel the Service without paying a cancellation fee during the Return Period, which is 20 calendar days from the date of your order (30 days in CA). During the Return Period, you may cancel the Service for any reason, provided that: (a) you contact us to cancel the Service; and (b) return with proof of purchase any product purchased from T-Mobile.com, 1-877-387-4324 or 1-800-T-MOBILE as part of Service activation. Even if you cancel the Service and/or return your product, you must pay all Services and other charges incurred prior to the cancellation or return. A product returned with proof of purchase to the place of purchase within the return period, along with its original packaging and contents, is eligible for a refund of the purchase price if it is in good working condition. . You may need to pay a restocking fee. The purchase price of your product may have been subsidized to facilitate your subscription to the Service. If you cancel service within the return period, but do not return the product in good working order, you will be charged for the subsidy amount received.