Bad customer service

I took the car in to be checked at Renualt as there was a shortage of oil in the engine,which was suprising as the car had been to renault about 2 months ago for a full service where the oil was supposedly checked. On friday the 17th of November i took the car bavk to Renault for them to check for me and advise as to why there was a shortage of oil. When i came back to collect the vehicle later on that day they had initially charged me about R800 for checking the course of loss of oil which they found nothing on vehicle and said it was negligent of the customer for not checking.We were then asked to speak to the service manger whose 1st comment was i "hope this is a civilised conversation" who then told us vehicle was not under warranty that is why we are being charged.The policy says any vehicle coming in for repairs which is not covered under warranty any mechanical repairs or part replaced customer must be called for authorisation which did not happen.The vehicle had been booked in for a major service with cambelt like 3 months back and was not charged because its under extended warranty.I do not understand why it would be then charged for something as minor as checking for cause of oil loss.The invoice given to us implies the vehicle had either been taken forcefully or ******.The service we received from the dealership management was discriminating and insulting. On Friday the 24th i got a call from Venesh the dealer principle to enquire about my complaint and he promised to get back to me uo until today i havent heard from him or anyone else from Renault. Prior to the call from Venesh i had called customer care where i spoke to Bonnie and she promised to get back to me but never did up until today. I need someone from Renault to call me and keep me updated on what is happening.