Sani Sixt Cape Town car rental trying to fleece cash out of customers

Cape Town Airport Sani Sixt Car rental. Company held my deposit for 3 weeks without releasing, despite numerous calls promising to release. A month after the car was returned, I recieved an invoice for R1500 for damage to the "luggage cover". They sent pictures of 'damage' - cant make anything out. Obviously a battling company and trying to fleece customers out of extra cash. Will never use again.