I was told the wrong information

I picked up a car from George Airport and the lady who was checking it out for me her name was Jackie (White pregnant lady). I enquired about the usuage of extra kilometers, she told me it was R1.98 per km and that I must bring the car back empty. Now that I receive the invoice I am being charged for petrol which I wanted to avoid by filling up because I know that is the standard procedure, but I was told not to if I will travelling extra km's. I do not have the money for this.