If you need to change your credit card or update an information on your credit card such as the expiration date, you should go to Billing & Payments->Payment profile and after you make the necessary changes, your should click the Change button.
I tried to buy more credit but it was declined. Why money is taken from my bank account?
If your credit card billing address has changed or your credit card is renewed with new expiration date or CVC, your transaction may be declined even when the credit card is valid and you might see this transaction as a charge in your bank account for a short period of time. At these times no money has been taken from your bank account. What you are seeing is simply an authorization, and this was reversed when the payment was declined. Please be aware it may take your credit card company a few days to clear the authorization. This transaction will completely disappear from your bank account in couple of days. Please contact your bank if need further information, they will be able to confirm the money has not been taken.