I have a Samsung galaxy s 8gb. Recently I asked o2 to unlock it from their network as I wanted to sell it because I didn't get on with the phone. They said I would receive a text in a few hours with the unlock code. No code came but from that point onwards my phone wouldn't recognize the o2 sim or any other sim. After ringing them again to see what had happened and my phone freezing totally they advised I needed a replacement. The replacement came in a day and I tried my sim in it, the same was happening, error message 'not registered on network'. Rang again and I was sent another phone and replacement sim too. Tried them both today and exactly the same message! Please help!