Unfair Fuel Charges from my deposit!!!

I have just finished a vehicle hire through Europcar. I paid a deposit of R1450. When they delivered the vehicle to me, I and their employee did the full inspection of the vehicle and I asked him what the deposit covered. One of the things he mentioned, was, if I returned the vehicle without filling it up, then they would use funds from my deposit to do so. So, on the day that I returned the vehicle, I made sure to fill it up. I went to the petrol station nextdoor to the panel beaters where I left the vehicle for Europcar to collect. They made no mention of charging for collection. Now, I get my deposit back, and they've deducted R154.86. I called to query and they told me it's for petrol. I explained that I filled the car nextdoor to where they collected. The employee said that they filled it up again, so that the next customer gets a full tank? Now, firstly, I don't feel that I'm liable for any fuel charge after I have dropped the vehicle off. Secondly, I didn't charge the Pinetown branch for the petrol they used to bring the car to me in Westville, so theoretically, I didn't get a full tank. I feel that Europcar are taking advantage of having a deposit to use and that is theft. I don't know how I can spend R197.32 making sure the tank was full on return and then 2hrs later, you manage another R154.86???? Even if I was responsible for that, which I still don't believe I am, R154.86 petrol charge between Mt. Edgecombe and Umhlanga is insane!!! Won't be using Europcar again!!