Inferior parts and service.

So it appears a sportage front brakes last about 30,000 kms based on my history. My problem is now on the 4th set, every second time you have to replace the discs as well. Today's quote R6700 odd on 129000 kms. There is still 20 % pad left. So why are the discs being " pitted, scaped" etc if there is still 20 % pad left. I assume the pads are inferior and have some hard substance in which scratches the discs. The second replacement Kia did not charge me labour ( after a major argument) but this is getting ridiculous. Then I'm told only use genuine parts and told all depends on how I drive. Kia head office last time showed no interest in my case . Brilliant car but inferior quality parts and no goodwill in handling complaints. NE13977/FK99RGGP