have you contected the operator which has locked the device to give instructions how to unlock it?

Just to avoid scenarios that someone pays 1euro for operator locked phone with false identity information (ie not going to pay for monthy fees), and then sells then cheaply to next owners who don't know how to unlock. In any case operator should be able to give you step by step instructions howto unlock.

And are you sure that your really operator sim locked, and not trying to unlock the normal lockcode (which is easy to do). Can you give some screenshots of error messages when your non-operator sim is the device?