You will talk to a CM. The number you call is a Costco travel number but it will eventually connect you to a CM once you go through the menu and choose the
Disneyland Resort. The survey you get at the end is a Disney survey and asks about how well the cast member did. I called a month or two ago about changing my last name on the reservation (got married since I booked the trip) and then again a few weeks ago about a payment method not working. Both times I called the Costco travel number and spoke to a CM and were able to fix everything I needed. This will be trips 3 and 4 through Costco this year and no complaints. I love the gift card bonus and I've stayed both on-property and off with a Costco package.