False adverti*****t by dealers

Hi I bought a Toyota Corolla as the dealer said and advertise on the window the car is light on feul it gives7 liter to 100km ant the specs6is showing 6.9 km to 100km The tank capacity is 55liters I drove this car and did not get 500km per tank I took it back to the dealer and he said I must drive it to the next service I full up the tank and get less km per tank. I have arrange for the car to be checked by Algoa Toyota and acording6to them there is no fault with the car I must take it up with the dealer The dealer is not willing to assist and Toyota claim is not there problem Is this not false advertising as we think we buy cars to save fuel only to relise we are been misleaded as ee6 do not get 11 liters to 100km