A bomber jacket that tore badly from just one wash

We bought a winter jacket for my son last year winter and it was big. Saturday was the first time we made him wear it. He wore it for atleast 2 hours, then Sunday we washed it and it tore badly on the side stitches indicating a factory fault. When we returned it to the store they said they can't take it back because it's last year stock. It was the first time he was wearing it and we even have a price tag to show that it's still new. Truworths is very pricey for them to treat their customers like that.