I had the same issue. Keep trying the site till it works. I bought an off contract tmo version from motomaker, was greated with the same message on their site, and recieved the same responce from support.
After I refused the responce from their support and told them only att and vzw don't qualify, the rep did research and came to the same conclusion. Basically, if you paid full price, you should be able to unlock. As I was waiting for him to come back to the phone, the unlock website worked. I guess the 10th time was the charm
. Keep trying and push back on support if you need to call in. Good luck