Rear brake failure on Mazda Cx5

My vehicle went for the 15000km service at Centurion Mazda in December 2015.The brake pads were inspected and showed the front brakes at 8mm, and rear at 6mm.No problem mentioned and no noise coming from the rear wheels.About a week before the 30000km service, the rear right wheel started to make a squeaking noise.I booked the vehicle in at Mazda Menlyn,I informed the service Advisor Niclole of this.She informed me that the brakes at the back were worn down and that it had cut into the discs and they will need to replace them and skim the discs.This all occurred on the 16 March 2016.Nicole then called to say that the Parts would be able to assist by Tuesday the 22 March 2016. Not happy but accepted the excuse,on Wednesday she called again saying that Mazda SA has informed her that the parts were on back order from Japan and that my vehicle will only be ready by 14 April 2016, which obviously was not acceptable for me.If the vehicle is under warranty, and this is not a driver related cause, this must be repaired under that warranty.I need urgent feedback regarding the way forward and suggest that you look into the cause of this problem from the manufacture side,not the driver.