Dishonesty from workshop

My car was due for its annual service, covered by a service plan. As I was aware of the fact that I needed new break pads, I checked beforehand if this was covered in the service but it wasn't. I therefore had then replaced privately, meaning my car went in for its service with brand new front break pads. I received a call during the day to tell me that they wanted to replace my front break pads at a cost of R1500. I feel that they were attempting to cheat me and thought that they could do this because I'm a woman. I still have the receipts from the front break pads as proof that they were replaced. I have heard stories like this but this is my first such experience after 5 years at this dealership. I will never bring my car back here again.