You need to keep rebooting the phone with the new sim until it comes online
If it doesn't in the next hour
You need to call O2
You can use Skype to call.
All numbers including Skype are in this guide
Advice from an O2 Guru regarding a way to get through:
When you call, you will be asked for the reason you are calling,
Stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to an advisor.
Press Upgrade, Lost/Stolen or Fraud if you have to.
8am is the best time to call
Track usage, upgrade and get support with the My O2 appDownload My O2