How can get a ZTE Blade A100 ZTE to prompt for an unlock code?

[MrRadio]

Bought it at ex Comm games auction to replace my very old HTC (to sit on my desk for inward only from ppl I don't want to annoy me). Put my working Aldi sim in and nada. It seems that it is locked to Optus. Took it to Optus shop who conducted tests. My sim works in their phone and other test phones, their sim works in my phone and another Amaysim sim work on the phone. Telstra sim does not work. They concluded that it was locked. They couldn't generate NUC so it was referred to "back end" who did gererate a NUC after confering with ZTE and emailed it to me FOC (I have two phones with them). The problem arises that according to Optus, Google and many other NUC pedaling pages the phone should prompt for code as soon as it is powered up with the errant sim. It doesn't, I have tried various keystroke suggestions found on Google but no joy. I would welcome any suggestions.