Need to unlock a device? Here's some information to get you started.

Good luck with the BBB and even the FTC won't help you. It's because you are going after the wrong people. Carrier with the way Apple or any OEM doesn't do affects the unlock process

Carriers can't unlock devices that they don't have in their database. The only way to put IMEIs into the database is from the manufacturer. This is to prevent fraud and theft. Since your device was sold by Apple and locked to T-Mobile 100% Apple didn't give the new IMEI to T-Mobile and that's where the disconnect is. This has been happening since the Apple Reseller Flex Policy, and how OEMs in generally rarely give IMEI of devices OEMs sell on their own without giving those IMEIs to Carriers. 

With the current process I will always tell people buy unlocked especially for iPhone as there is no difference between unlocked and a carrier branded one. Android devices mat has slight differences in carrier aggregation but it's all marketing as most servers top out way less than the bandwidth you can get. You will always get the fastest the slowest speed is willing to give you. You can have 1 gb speeds but the server is only able to give you 50mb well you only getting 50mb. Speed tests are fun and all but not realistic in real world usage.