Wanting to Blacklist Me for their Admin Mistake

Rented a vehicle in June from OR Tambo. First vehicle had clutch problem, had to exchange it for another. Then got windscreen chipped on highway to Pretoria. Having not taken the additional insurance, this turned out to be a costly exercise when I was charged R3 667 for a Hyundai I10 windscreen. This was deducted off my R9700 deposit I had to pay when collecting the vehicle and the rest was paid back after huge delay. Then the sms's and phone calls started that I am in debt for the R3 677 and that I should pay without delay. I explained to the lady calling that no monies are owed. She promised to correct it on the system, but to no avail; the letters and sms's kept coming. Eventually I wrote an email to Europcar explaining the whole situation. Today 4 months later I received an email from attorneys, on behalf of Europcar. If I dont pay within 10 days I will be blacklisted. Again I phoned Europcar, again explained, again I got the assurance that its their mistake and I don't owe any money. Promises were made to email me back as proof. I am still waiting. This is the worst customer serviced ever. I will not use them again.