Irreparable suitcase under warranty

I bought a suitcase three years back and the zip got broken. I took it back for repairs because of the 5 year warranty but it came back with amateurish stitching. My second Cellini suitcase also got broken last year, I took it back and the zip was replaced. I then took back the one with the stitching and asked that the zip be replaced too because I can’t use it anymore with the stitching. I was told that their machines can’t replace zips on this size suitcase. What must I do? Why do they sell things they can’t fix under false 5 year warranties? Must I throw it away because I can’t use it?