Sounds like you got a bad (or just lazy) Reservations Agent. I'd call back and try again. A decent will realize that something is very wrong and want to talk to a Supervisor. If that doesn't happen, ask for a Supervisor yourself.
Note: I used to work at a travel call center. Make sure you ask for a Supervisor or "someone that can fix the problem" and not a Manager. Supervisors are content-knowledge experts. Managers manage people and therefore might not have the same skills necessary to fix the problem. That's just a little insider trick I learned. I'm assuming Marriott Central Reservations has a similar structure.