Help with unlocking a T-Mobile M9?

Hey all, I have an M9 on T-Mobile USA and would like some help unlocking it. This phone is a replacement device, due to my last M9 having hardware issues. (Constant crashing.) I initially contacted T-Mobile, and they had told me that they could not unlock my phone due to it being a replacement device, because they wouldn't have the unlock code. They told me to contact HTC about it, which I did. HTC told me that there wasn't anyway that they could unlock the device because T-Mobile would have the unlock code. I'm just sorta confused on what I should do right now. Is my device really going to be permanently locked to T-Mo?