Useless service ever

I hired a car from avis from the 31st dec 2017 to 02/01/2018 when I took the car from avis the car didn't have full tank and I notified the lady that did the booking for me and the guy that was checking the car for me I was told to take the car and bring it back with the amount of fuel I took it with and that's what I did but then they decided to charge me for fuel now i have lodged a complain and they said it will take 2 days to reply but it's 6 days now no reply when I phone them I'm made to wait for ever i hate they service it's **** my reservation number was ********** 86 **** service ever