Car oil service Complain

Good Day Sir/Madam On the 31/08/2017 my car was booked in for a oil service at BMW Auto Glen.The service I received particularly from Francois Van Rensburg was on point,however it came to my suprise as I was driving to work on Thursday 28/09/2017 the oil Light came on on my Cluster.I pulled over at a Bp Garage in Fourways crossing to check the oil level with a Garage attendent and I was shocked to see that there was absolutely no Engine Oil and I was very shocked given that I had just serviced the car in August and my car has no Oil leaks.I then decided to Call BMW Auto glen to inform them about this problem,the lady said to me that I would have to re book my car for a Diagnosis to pay an additional R1100 for them to check the car.I said to her how possible is it for a car to be serviced and hardly a month later the oil light comes on? It means that someone did not do their job correctly.I paid for them to service my car and I expected a World Class service from them,but no that is not what I got.I am extremly dissapointed and Angry,my consumer rights have been violated by this.I will be escalting this complain to their Head office.I cannot pay for services and not get quality resultsbas they proclaim they offer.This is preposterous,i had to incur additional expense to buy Engine Motor Oil.The reason we take our cars in for servive is for peice of mind knowing that our Engines will be well maintained.