Shocking attitude in the service industry

My husband and I went on an anniversary weekend away in November 2014 down to Cape Town. We arrived on the Friday - picked up our car from the airport - and left again on Sunday after dropping the car off. Whilst waiting in the departures que - I got a call to advise that the antenna to the car we rented was missing. I told him I thought this was strange - since we had not noticed firstly, had been listening to the radio secondly and the car had been inspected before we left. The gentleman advise he would get back to me. I then called them on Monday and spoke to the manager who advised me that the antenna was indeed missing. I told him that I was shocked at this happening. He said it seemed to be a recurrent situation in Cape Town currently and he had experience another two clients with the same issue. I told him that considering it was a regular occurrence - perhaps clients should be warned about this - so we can remove the antenna ourselves to avoid it. My deposit was paid and I heard nothing further. I have now received two threatening calls from the Tempest branch in Bruma threatening legal action if I do not pay the R285. I was NOT NEGLIGENT in any way - and refuse to pay.