incorrect charging/

Good Day Sir/Madam I rented a car with avis car rental last year September till October I took the car from Avis Cape Town International airport,I took the car from the 06 September 2016 till 2 October 2016 On the day that I took the car contract was opened by Ayanda the guys name and the rental was from 6 Sept till 8 Sept Below is the transactions amount that I received from Avis customer serice 06-09/2016 R2853 Auth code 908592 10-09-2016 R2550 Auth code 901445 17-09-2016 R3300.18 Auth code 203795 25-09-2016 R2778.93 Auth code 203795 22/10/2016 R288.99 Auth code 406405 The total is R11 771.10 When I returned the car it was the Sunday 2 October 2016 at 23:00 contract was never closed was told someone will call me, on the following day the 3 October I made a follow up and was told the car is being checked and there is a dent then I said ok, later on the invoice was sent to me of R4500 with a invoice of R17000 and some odds, then I told them am not owing avis R17000 am only owing the 6200 witch is for car dent R4300 PLUS Full tank and extra two days that the car was late with because it was suppose to be back on the 30 September 2016, I have been at cape town branch but no one is willing to fix this as am asking them if they saying am owing the R17000 that means I got the car for free from day one, I never paid the deposit staff like that because with Avis they don't give you a car with out money and rental agreement, its almost a year now still waiting but nothing has been done and I have spoken with Patrick one of the branch managers also he cant explain what happened writing on hello peter is my last resort ********** 00