Europcar shocking business tactics

I recently rented a vehicle online with Europcar, the whole rental was a mess from the minute I landed and went to the office. They demanded a credit card and told me that wa the only way to get the car. Even though in my email confirmation it said I could use either a credit card or debit card. Eventually they agreed to use the debit card after fighting for nearly 30 minutes with them. They then took off -6,470.81 on my debit card and promised that if the vehicle was returned with no damage, the amount would be sent back within a few days. This was told to me by the manager of the branch at Cape Town international airport. I then get a bill today that I owe Europcar a further R3492.00 I firstly want to know what this is for, when you have al;ready taken R 6470.81 on top of my original rental that I agreed to when booking of R2978.81. I demand my deposit in full be paid back to me and if one more cent is taken off I will not only reverse the transaction with my bank, I will be contacting my attorney to take action for my refund. This is disgraceful, the car was taken back in perfect order with a full tank of petrol. I await your reply in this matter.