This should be a fun one to break apart.
Ok, so if you tried calling them you would have realised that they have set phone times for calling it. You would have been told this by an automated message.
If you were still up at 10pm then you would have seen the message clearly stated on their homepage.
You would have also been notified of the status page:
http://status.o2.co.ukThanks to them working overnight, they're slowly restoring the service.
Be a bit more patient and it'll all work out for the best.