AVIS *****ing loyal customers!

I had minor damage to a rented AVIS vehicle in January, agreement E***. I forfeited my deposit and paid R6000 in total. The damage to the vehicle cost AVIS R750 but AVIS is demanding R12000 from me!. I'm refusing to pay this amount as it is unjustified. AVIS has sent this to their collection lawyer. I used to rent 4X times a month (R4-6k per month). In the 8 months since this incident, AVIS has lost at least R32000 in revenue pursuing a non-existent debt of R6000! Shameful and very bad business practice