Solved, thread can be closed.
I bought today Orange prepaid, created the contact with the unlock code as a number. Performed a call to this contact but there was only a message that the call failed. I left the phone with Orange sim for a couple of hours.
I started looking for other solutions but for some reason I hot-swapped Orange sim to my beloved-locked prepaid...and it works.

Strange thing that there was completely no message that phone was unlocked when I performed a call to unlock code Actually in the instructions there is statement that unlock code can be only inserted once and I called this dummy contact about three times.

Strange, but happy.
Thanks to: immi.shk, eres and rainisto. Your replies were inspiring!