"I apologize that you had not received your item. I wish I knew what happened. I have refunded your ... " (more)credits, and of course if/when the card arrives, please keep it for your inconvenience. Thank you for letting me know you had not received the card."
"i apologize that you have not yet received your item. It had been mailed out many days ago. I have ... " (more)refunded your credits and when you receive the card, of course please keep it for your inconvenience. Thank you for letting me know about it's slow arrival."