Hi MI5, I've tried online and by phone. The only other option is to go
to a store. That's absolutely not convenient as I live miles away from
an o2 shop. I guess I'll have to get a new sim with another network.
I’m having exactly the same problem! I've tried two different cards and
calling 4444. It goes through the whole process by phone and online then
says unable to process payment. losing patience now!