EDIT: Turns out they called Andrew's phone number instead of mine with an automated confirmation, and apparently he must have cancelled the appointment. He was the original owner of the account when he was living here, and supposedly transferred the account to me when he moved. However, Comcast, even though MY name is on the bill, still had Andrew's email and phone number as primary. I was in their system as "Service Admin".
After a lengthy Twitter conversation with a representative, I think I've FINALLY got the account straightened out, getting all Andrew's information removed. A new service call is scheduled for Wednesday between 1-3pm. Hopefully I'll be home from my "post-op" appointment at the hospital by then.