Doesnt wanna account for a Factory fault

Im very dissapointed in the quality of rochester furniture and their services.i bought 3couches from them and one of them was faulty.it came with a missing arm support.the arm support on the one side was just a box.it looked fine,covered nicely you wuldnt even notice.until wen time went by and it started sagging i then realised it wasnt supported from the inside by the wood like the rest of the couches.i went to the store in kemptonpark wher i bought it and they promised to contact me but they never did.went back again until the 3rd time i went they finally called and arranged for the couch to be fetched.it took about 6weeks they never said a thing to me.i started to make a followup with the store.ive been told i need to be patient.until 8weeks later when they called me and said unfortunatly i need to pay R1400 because the couch does no longer have a guarantee.i noticed the faulty after a long time.they even agree that the couch is factory fault but now the problem is i ddnt notice the fault immediately.yes i ddnt notice it immediatly or within days bcos it was covered with a box that made it look ok until the box started sagging.i dnt understand why they cnt account to the fact that is a factory fault.they can clearly see that the couch is not broken or damaged but the support wood is simply missing.why must i pay for a factory fault.im very dissapointed i wuldnt advice anyone to buy their poor quality furniture.