Received the unlock and unfreeze codes within 5min of purchase. The code did not work, so I put in contact with the customer service by email.
They double-checked first that the unlock code was introduced as indicated (which it was the case). Once replied, they provided me with a satisfactory solution as they emailed me detailed instructions on how to unlock my device by following a different approach, again all this within 20 min.
Now I have an unlocked mobile phone. Thanks lads, good job.