Europcar- Bad billing practice

I did a walk in at Cape Town International Airport at Europcar for a vehicle. The only small vehicle was a I20 at just under R900 per day so dont know where the advertising that they have cheap rentals. I used my credit card and over R7000 was put on hold on my account. I was told when I return the car the transaction would be cancelled and only the actual amount charged to my credit card. We returned the vehicle as per the agreement but the amount of over R7000 has been processed. When I contacted Europcar I am told they will pass a credit for the R4000 plus which is the difference between the holding amount and actual but it takes up to 10 working days for the credit to processed. Not acceptable as you can calculate how they are benefiting with the interest on the amount and in addition I was told I would only be charged the actual. I have rented vehicles in the past with other companies and have never experienced this. No Europcar for me again