Account handed over without response to my dispute letter

I have been billed incorrectly, I have sent formal letter regarding my disputes on the costs. I have spoke to staff member several times, no one has come back to me telling me that why I need to pay for this costs because I stated my reasons in the dispute letter. Now the account has been handed over to the lawyers. I find the customer service is very poor, no one is willing to assist but shifting the blame. I never refuse to pay but I wanted someone to explain to me that why must I pay for surcharge cost because it wasn't my fault that branch didn't have car I wanted and it is the branch which told me to go and get the car from their alternative branch without explaining prior that they are going to charge me for that because I would refuse. I believe that I was treated unfairly as the Europcar loyal customer. I have been using Europcar for the very long time but service I received recently I find very unprofessional. I am taking this to Discovery as well. We are using Europcar because they're associated with Discovery. I am very disturbed with the poor customer service I receive in them.