Seriously, I spent about 5 minutes trying to debate why my payment was being declined and it probably had something to do with the person on the other line running rubbish through, such as a start and expiry date that wasn't close to what I said and not taking my card name correctly (as it has been changed by the bank to fit on the card), so eventually I just gave up and put the phone down.
I will probably end up trying again after my direct debit and statement dates as well, mainly because I don't want to end up with no money next month (I have a direct debit that pays for my full card balance monthly).