The mistake you appear to have made is flashing firmware to an unlocked phone.
Any phone on the 3 network would be subsidised and the price you pay is to be locked to the network.
Unfortunately the only backup that would have been useful in this case is a nandroid (through CWM)
This would have kept a full copy of your original firmware and apps.
What I would do?
First thing is can you get into download mode? If so you have a chance.
Download this UK 3 firmware and flash with Odin:
[ Login above or register to see download links. ]
This should restore your original firmware, so that you can start again - with an unlock
