I have just tried, both web-based from a pc, and on the android app.
The PC gives me the following error when I click on the link to top up by credit card, I cannot enter any details;
Sorry, you have been blocked from using the payment system.
You have been blocked from using the credit card payment system. If you believe this has been done in error we apologise for the inconvenience. Please contact us on 777 from your mobile or 0800 800 021 and we’ll sort it out.
My phone allows me to enter all of my CC details, however has the following error after submitting;
Sorry, there was an error processing your transaction.Please try again or call 777 customer services.
Unfortunately I am in no position to call them until after 10pm.