For some reason CYDIA is using an old expired credit card. There is no way to change it (that I can find) in Cydia. Cydia is using Amazon payments and that card isn't even listed in Amazon Payments any more (it expired). Because of this I can't make a purchase and I see no way to change the card. Can't even find a way to contact Cydia to ask (and from what I have heard the chance of getting a reply from them is zero to none anyway). I guess I could create another account but then I'll have problems reloading previous purchases.