Disappointed again!

Again I have been disappointed with Fury Ford Amanzimtoti. About two years ago the widscreen wiper system stopped working. The technicians spent a couple of days trying to fix it, and eventually replaced a part. Subsequently, the windscreen wiper system has stopped working again, although this time the vehicle is now out of warranty. They have quoted me to replace THE SAME PART at a little over R4000, but now I have to pay for it as it is deemed NORMAL WEAR AND TEAR! How long are windscreen wiper control systems supposed to last?