Servicing Department Push backs

We had made an appointment for My Nissan Navara double cab ( CXG 551 L) to get its 90000km service this morning. They said an appointment is not necessary as they take the first car to arrive. We received a confirmation sms and we were in front of the doors this morning at 6:30, they said they open at 7:00. Usually when we are this early we get the vehicle at around 12:00, but today they said we will be pushed back to 62th in the row (according to our card) and will only get the vehicle at 18:00. One of the ladies informed us that they have overbooked for today and a manager tried to make it out as our fault. This is unacceptable as we are on our way on holiday and have a a long way to travel still today.