I'm sorry about the issue. What's the model of your Kindle?
You need to sign in with the exact email address as registered on the Kindle. On the Kindle, you can go to the Registration / Account option in order to confirm your email address.
Then go to the website below:
, and sign in your Amazon account with that email address (if you forgot your Amazon account password, then use the Forgot password ***** at the above website)
, then click on Settings, then click on Edit Payment Method and continue there.
Please reply at the box below to continue troubleshooting. Thank you.