Just to let people know if you find the updating credit card details doesn't work, as it wouldn't for me do not choose the update account details options on the support line. It simply says use the portal, which is broken, and then hangs up!
In the end I had to pretend to have a broadband fault, where is the any other issues option when calling (I can't find it). Wait 20 minutes to talk to a service person who was bordering on the rude (as I was calling the fault line to get my details changed and wouldn't believe the web site wouldn't let me change it).
I'm curious as to why you couldn't update the card details via the portal. What was happening when you tried entering the details? Did it give you an error? Or was it just that the card type you have wasn't listed (e.g. Switch/Maestro, Visa Delta/Electron)?