problem trying to unlock U5

I am trying to unlock this U5 via codes.

I bought codes from Sony ericsson Service, got NCK, and other codes.

Phone says there are 6 attempts remainng, I enter code, and it failed.
counter downgraded to 5, but now I cant enter the codes again, when I insert the code or any 16 digits codes it will not response to the code, it just will put me back to the previous screen, where I select option to enter the code, it asks again and then the same thing again and again,.

I flashed the phone and get the same results.

Any suggestion? it st8ill says there are 5 attemmpts remaining