How do I unlock my s6 edge from tmobile when it had no unlock code?

[Eric Smith23]

I have a t-mobile s6 edge. Purchased through Amazon unlocked . I switched to at&t with a clear contract. Now it's locked into tmobile. There is no unlock codes for this model. And the provider will not unlock it due to I am not the original owner. I tried cellularunlocker.net- didn't work. I'd love to get this done for free but I will pay an app that's proven. I don't want to buy a new phone. PLEASE HELP!