Making me pay for brakes on a new car

I own a A*** model that I bought from Mercedes. 2 weeks ago I took my car to merc constantia kloof cause it was due for service and it had a loud noise when braking. No warning lights had come up. 1 week and a half later I was told Mercedes South Africa wasn’t going to pay for my brakes cause the brake pads are finished and the rubber was completely worn out. My car is under warranty and motor plan. My rear brakes have never been replaced. This is my 2nd service with this car. There was no warning light that prompted me to check my brakes which means this car is not a safe car to drive then secondly when I took it to Mercedes they say I must pay for it as if it’s my fault. I’d understand completely if I had ignored warning signs but there was no warning to say my brakes are getting finished. Now Mercedes wants me to pay for the replacement of my brake discs and honestly this should not be my cost. I cannot buy such an expensive car then also be expected to pay for parts and maintenance on the car. This is ridiculous. Now I’m scared for my safety as well as inconvenienced by a company I used to look up to. Why won’t you put senosors on the car brakes??