I am not sure which promo you were specifically going for but based on the information I will assume it was this one. I copied and pasted the detailed below for how to qualify. I am sorry that you were misinformed but there is a positive here to remember which is always check the fine print and get written evidence to verify everything is correct. As far as what you can do in your situation, you will need to work with the T-mobile T-force team as no one on this forum can make account level changes. Since this was not handled correctly I am not sure what they will do for you but maybe you can get someone that is higher up that has the authority to make a executive decision. Even if it does get resolved you will not be able to just leave since you would owe for the phone on the spot as the phone is paid of in the the form of credits if I understand correctly.
Again I am really sorry I can not personally be of more help to you as I'm just a fellow customer, but at least I can point you in the right direction. The one other avenue you have is to message the CEO directly about your case his email is John.email@example.com
Here is the link for where I got this information as well Recently expired rebates
2018 Q1 Samsung BOGO Offer
Buy a Samsung Galaxy S8, S8+, S8 Active, or Note8 and well-qualified customer's can get another Samsung Galaxy S8, S8+, S8 Active, or Note8 on us (of equal or lesser value; $750 max value) by rebate when both devices are purchased on an equipment installment plan, you port in at least one number on a T-Mobile ONE or select Simple Choice Unlimited with unlimited high-speed data plan, and trade in at least one functional, paid off, eligible iPhone, LG, or Samsung device. If you cancel wireless service, remaining balance becomes due.
- Promotional Window: January 12, 2018 - February 27, 2018
- You must meet all these requirements during the promotional window:
- Purchase two new Samsung Galaxy S8, S8+, S8 Active, or Note8 devices on equipment installment plans.
- Port in at least one new voice line onto an eligible rate plan to be used with one of the new devices.
- Trade in an eligible device:
- iPhone: 7, 7 Plus, 6s, 6s Plus, 6, 6 Plus, SE, or 5s.
- LG: V20, G6, or G5.
- Samsung: Galaxy S7, S7 Edge, S7 Active, S6, S6 Edge, S6 Edge+, S6 Active, S5, S4, Note5, or Note 4.
- Submit a request on the T-Mobile Rebates page (including IMEI entry) using promo code 18Q1SAMBOGO within 30 days of second device purchase.
Tax on pre-rebate price due at sale. Limited time offer; subject to change. Qualifying credit, service, port-in, and finance agreements for both devices required. GS8: $30 down and $30/mo. x 24, pre-rebate price $750.00. GS8+: $130 down and $30/mo. x 24, pre-rebate price $850.00. GS8 Active: $130 down and $30/mo. x 24, pre-rebate price $850.00. Note8: $230 down and $30/mo. x 24, pre-rebate price $950.00. 0% APR. If you cancel wireless service, remaining balance becomes due. Max 6/account. Rebate up to $750 on device of equal or lesser value via prepaid MasterCard® Card. This Card is issued by Sunrise Banks N.A., Member FDIC, pursuant to a license from Mastercard International Incorporated. Mastercard is a registered trademark of Mastercard International Incorporated. Use of this card constitutes acceptance of the terms and conditions stated in the Cardholder Agreement. Cards will not have cash access and can be used everywhere Mastercard debit cards are accepted. Must be active and in good standing when card is processed. Allow 8 weeks. May not be combined with some offers and discounts (e.g., Carrier Freedom).