i would say they maybe ment fronts were 8mm and they rears are 0.8mm ?rears can wear quicker especially as rear calipers can seize!!would say they have not replaced your pads with a different set when u took it back for a second time!sounds like judging by your description they might of just deglazed them and put copper slip on them!giving that rust colour!!after market pads can sometimes by noisey as well!!