I don't know why tmo_mike_c censored out the version numbers but...
To me, it sounds like the phone you had was "soft jailbroken", meaning the person who you bought it from may have rooted the device to install a version of the radio that bypassed the unlock check. When your device updated, this was also updated to the proper version that checks to see if it's been unlocked.
This appears to be fairly common with iPhones, but I must say this is the first I've heard of it with Android in the forums here. It wouldn't surprise me, though.
To get it, you must be a T-Mobile customer, or contact the person who you bought it from to obtain the code for you.
Thanks for the advice.
Where can I find the email support service?
I have read that there is a problem of the iPhone. But I have a Windows phone.
For iPhone there are advice to contact an outside mediator.
But I have a very old model phone worth $ 15.
Pay $ 30 for unlocking - there are stupid.
It has passed more than two months after purchase and warranty from the seller end.
Following branch support staff? What should I do? Phone put the bin?