Amazon Marketplace Account Closed After Credit Card Verification Failed

My Amazon Marketplace account was closed today and there is a balance of about 20 USD remaining on it. When I try to log in, I see a message stating that my credit card information cannot be verified, and due to this my account has been closed. I have not been given any clear explanation beyond this message and I am unable to access my balance or use my account. I also cannot reach Amazon customer service through the usual channels, so I am currently stuck without any way to resolve the problem or withdraw my money. I request that my account be reviewed urgently, that a clear explanation be provided about the closure, and that either my account be reactivated or my remaining balance of 20 USD be refunded to me as soon as possible.