ATT, Samsung Note 4, unlock code does not work, now what's next.

I bought an ATT Samsung Note 4. Never used due to a trip to Asia. When I came back, family plan had switched to T-Mobil. I then contacted ATT for the unlock code. When I got the first code, I tried to put in the new T-Mobil Sim card to realize that my device does not boot up. Brought the device to ATT repair center to be told that the 14 days replacement period is over and was advised to send to Samsung for repair which I did. When the phone got back in my hand, I submit the 2nd unlock request online, got the code, which is the same with the first time due to same IMEI. tried input the code 4 times with same error message: device unlock UNsuccessful. I called Samsung again, and conferenced in with ATT tech support. After 1 and half hour, I was told to wait for an email and 2 days later, I received the "new" unlock code which is the same like the ones before. Seems like my phone is locked to ATT network without me reaching the 5 tries allowed by the administrator. Now I have a brand new phone paid off ($600) and cannot be unlocked to use with different carrier. What is my next step?

Any advise from the community would be very appreciated.

PLEASE HELP.