Did they give you an actual site number when you booked? Many campgrounds are on a first come/first served basis regardless of when you booked. If you didn't call and tell them you'd be arriving late they may have assumed that you weren't coming (which shouldn't happen until the following day IMHO). Did you ask if you could move if a site opened up? If they made no guarantees then other than posting a negative review I don't think you have much to stand on especially since you didn't address the issue right away. As far as the person working on their unit, it may have been a safety issue or in need of fixing in order for the person to be able to drive away.