Poor customer service and Shoe quality

Hi there. I wonder if you could help me. I bought a pair of sketcher for my son a month ago and the material on the inside of the shoe has already frayed. I tried to return it to the branch at mall of Africa however they’ve said it doesn’t qualify as a return as it’s not a manufacturing fault. While I understand that it’s not stitching etc that has come loose I find it hard to believe that for the price we paid for sketchers the material is not robust enough to withstand 3/4 wears. I was with my son for most of the time that he wore it as we were on holiday and he only used it while going out and not for sports or school etc. it’s very disappointing that we’ve wasted so much money on a shoe that doesn’t last when we’ve spent less on a school shoe that he plays sport in and wears everyday yet we haven’t experienced the same problem with that. The customer service was also really bad as I spoke to the manager Chris who was quite rude and brash. He blamed my son for hooking it in something which is clearly not the case when looking at the shoe. While I understand that usually kids are hard on their shoes. Surely an athletic shoe made for sport should be more robust?