All forms of contact here so you'll have to keep trying http://www.o2.co.uk/contactus
Other options when in UK include O2 stores.
@Unbarred This is a customer community. No one here can help with account issues. It sounds as if you may have been sold a counterfeit sim card. You'll need to speak to customer service in the morning. https://www.o2.co.uk/contactus
Edit: Alternatively, you can call for free from any phone from abroad on +44800 032 1402