Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble, Kathleen.
This is best done from your computer, it doesn't work on the kindle itself.
Go to the amazon website, click on Account at the top right (sign in, if prompted)
then go here:
http://amzn.to/1NupYm0 (manage payment options)
there you can be sure your card/bank info is correct (right address, valid expiration date, etc)
From there, go here:
http://amzn.to/1N8muYQ (content & devices)
On this page, click on the SETTINGS tab at the top right,
then you can from there set a default card to be used for one click purchases on the kindle.
Under Kindle Payment Settings, click on the Edit Payment Method button, and you can set the card you want used for your kindle purchases.
After that, reboot the kindle by pressing/sliding and holding the power button for 20+ seconds, and it should operate normally from there.