Horribly frustrating problem with my new iPhone 4... UK only?

[Lucas]

I just upgraded to the iphone 4 32gb today at the 02 shop and traded my old 8gb 3g in with the sim card. (stupid woman behind counter didnt tell me to take it out). Anyway. I have got the new micro sim for the iphone but cannot connect to the 02 network. I have registered the phone by accident under wrong details so it wont work and now reformatting it does not allow me to re-register it. i rang 02 and they said register it then I couldnt contact them again. I cannot get to a shop until monday so what can I do to get on the network. I desperately need to be able to contact people. Plz help. I have never been so frustrated. Thanks