The best way to apologize is to let the customer vent first. Don't interrupt, just take notes and make empathetic noises. You can even tell the customer that it makes you mad too. Second, ask the customer what their speed of need is. Tell them what they ant to hear. That you apologize, that you understand how they feel, that you are meeting with the appropriate people to get a resolve, and that it will be done in 24-hours.
