They might simply forget to send the car. I had reserved a car the night before to catch the train on-time. I was at the door ahead of time and the car did not show up. When I contacted them, they said "nobody told us about this service" (and so I missed my train). I asked for some explanation and they said the manager is on vacation for the next few days. They said the manager will contact me and they have not returned back to me since then.
more