The advice that you got from the other two posts is spot on. Sorry that you had a bad experience, but I would say from my long experience with Marriott (>1000 nights stayed) that this is not typical.
One other thing to keep in mind going forward is that, if you stay at the same property routinely, get to know the GM. I stay at a specific Courtyard a lot (everyone knows me by name) and one of the few times that I did have a problem with Marriott Customer Service, I mentioned it to the GM while we were talking one day, and the next day Corporate was calling me to fix my problem and falling over themselves to appologize. It might not always work, but it helps to have friends inside the system.