Car not Full and then Charged for filling up after returning full

I got my car at George airport and reported that the petrol tank was not completely fulled up. But then I did the decent thing to fill up the Car in George on my way to the airport as I normally do with the other companies. Avis you suck. Then you charge me for filling up the car and 2.9 liters that your staff drove out. Instead of offering a discount because I did not get my car completely full this is unprofessional and Trust me I will not and neither will anyone I know or deal with in business with ever make use of you.