Hertz so bad!!

For business I have to occasionally travel and get a Hire Car. I always fill up my rental before returning it- as suggested by the staff when you receive the car. And every single time, I get charged a levy for filling the car, and an amount, albeit small, for fuel. I have used many different companies, and they all seem to do the same thing, presumably hoping people dont notice, or cant be bothered to follow it up as the amount isnt large. As this goes on my company card and I have to account for every transaction, I have to follow it up. A few weeks, and a few mails back and forth and the amount is credited to me. Except this time. I used Hertz Car Hire. Its been 2 months of emails back and forth. Ive been dealing with the credit controller who has been very helpful, admitted their mistake etc... but then referred me to customer relations.... who have not rep**** to a single mail. They must be the WORST CUSTOMER RELATIONS DEPT IN THE HISTORY OF CUSTOMER RELATIONS!! Hello- do you know what your job description is??? Do you get paid to ignore your customers? I will never use Hertz again- on principle. They had no problem taking my money but clearly have not intention of returning what they took " by mistake"