Auto boys

I recently took my Mazda for a service at Umhlanga Mazda. I received a call from there sub contractors to say I had 3 small windscreen chips on my windscreen which could be repaired by Auto boys for a price of R120 per chip coming to a total of R360. I was told that I could put the claim through my insurance company Discovery Insure. I agree and got authorization from Discovery. The repair was done and 2 weeks later I saw on my claims history that an amount of R4263.05 had been charged to Discovery for the chip repair. I queried this with Auto boys and Discovery insurance and was told that the amount quoted was if I paid cash however Discovery and Autoboys had an arrangement on the price that was charged for windscreen chip repairs. I am absolutely horrified by this. How could they quote R360 to me and then charge the insurance company over R4000 to do the repair. And what is worse how does Discovery insurance allow it. That why we paid so much for insurance. If I had know that was the amount that was going to be charged I would have never gone ahead with the repair.