Cheating Tempest car hire

I am VERY DISAPPOINTED with Tempest car hire !! I filled the tank AT king Shaka sasol garage, and handed the car back. I received to invoice to see that i have been CHARGED an extra R74 PLUS R20 odd admin fee for petrol??????? The tank was FULL when i delivered it!! This is ****************, and i will not let Tempest get away with it!!!