ZTE Z970 sim unlock???

Someone please confirm that Sigmabox can not unlock Version B33 of the ZTE Z970 from Tmobile. I just want to make sure it cant to stop trying. It was a real pain to root it. And when i finally managed to do it, i unlocked the phone successfully according to the log file on Sigmabox. But when it rebooted it was still asking for code. Also,, if that is the case, can i downgrade firmware on that phone to achieve unlock or is my only option to buy a code??? Please answer me on this ASAP. Thanks