Sim cards in Europe

hello all,

I'm in a bit of a pickle. I have a nokia mobile with a UK sim card (orange network). When I got to Germany my phone automatically switched to a different provider - O2. I cant figure out how to top up my mobile. I tried to buy O2 credit but it didnt work. Can I buy a different sim card that operates in all of europe?

Any advice would be great.
Regards,
Jannah

You're actually still with Orange, but the handset has roamed to o2. You still need to top-up as if you're in the UK on an Orange network. The easiest way to do this is online: here