Fuel policy..... Small print

After refuelling at the nearest fuel station to the airport Bidvest Car Hire managed to allegedly squeeze a further 1 litre after I dropped off. They then charged me for the excess fuel along with a Contract charge. This is despite pre paying for the car hire. After complaining they only refunded the fuel charge but not the 'contract charge'. They state that this is a charge as they have to keep records for 5 years??? This is not a local charge as they are now claiming. AVOID these companies that find extra charges. I will never rent from them again.