I'm sorry about the issue. What happened when you changed the credit card details in your kindle / Amazon account? Was there any error or message?
What's the model of your kindle?
Do you have windows xp, vista, or 7, or 8, 10, or mac computer?
Can we do a remote support session, so I can troubleshoot the issue directly on your computer together with you?
Please reply at the box below. Thank you,