Over charged by AVIS - terrible customer service - wish I could give them no stars - one star is too generous!

I booked a guaranteed model POLO TSI and was given a VIVO without notification. I was assured that I would receive a discount. Not only did I not get the discount I has levied additional charges! The car was filthy externally. I filled the car before returning it to the automatic stop and was charged a fuel filling charge and for 2,38 litres of fuel. This is how the treat their "preferred customer". No-one responds to email queries or answers their customer care line. Seems to be run and managed by *******. Don't use them - go somewhere else - anywhere else.