[mikael]

My mobile phone company handles that situation automatically by e-mailing to the client, informing them of the amount of the bill and that the credit card processing failed. The note provides the customer with a phone number to call in to resolve the issue. They may send multiple e-mails, or perhaps follow-up themselves with a phone call if the customer doesn't respond -- I don't know. I called in and got my card number corrected immediately.