Thanks for the question. I understand you are having issues editing the payment information on your account. In my experience, this usually occurs due to two common reasons (though there may be more):
When there is a mismatch between the iTunes Store's records and your credit card company's records, you will receive an error message stating that your credit card's security code isn't valid or that your zip code does not match your bank's records.
In most cases, this issue is caused by a formatting error in the billing address that you have provided. You can correct the issue by verifying that the information you have provided is correct, or by changing the format of your address to match the format that your credit card company has on file.
As with many other merchants, the iTunes Store and Mac App Store places an authorization hold on your payment card account for the approximate amount of any purchase you make. If you update your billing information, the iTunes Store or Mac App Store will place an authorization hold on your payment card account, usually in the amount of 1 USD or the local currency equivalent, to verify your account information.