Never use First Car Rental!!!

We hired a car 2 weeks ago from Lanseria Airport. No insurance was included in our contract. On arriving no-one check the car with us, because there was no one to assist us. The car was dirty and it looked if the front windsrean had a scratch. They just gave us the keys and off we go. Last week we gave the car back at OR Tambo. When we arrive there, we mention the company that we think there is a scratch on the front window. Yesterday we received a invoice of R 9000 on top of the deposit. How can a scratch on a window cost R 9000? My personal car had the same problem and it cost me R 300 in April. Could any one assist us asap.