Q: How do I speak with customer support if I don't know my serial number?

I hate to state the obvious but get your serial number then call them.

How to find the serial number of your Apple hardware product

If you live by an Apple Store just walk in and they can find you in their system that way.  Over the phone is a pain in the A

there are 2 ways. one in on the bottom cover. if is not there, cause is blurry or not visible, and you can turn on the computer, the serial is on about these mac.If the mac is not turning on, you have to take the bottom cover off. the serial number is located on above the ram slots.