To return school jacket consumer rights advice

[Itsallgoodimtold]

I bought the winter jacket in august from the single designated supplier along with rest of uniform. It seemed ok and I zipped it up on son a couple of weeks ago. When we arrived at school it got stuck half way down and after a lot of effort had to be removed over his head. Not worn since. Husband took it back but it kept working in the shop so he came back home with it. You can see that one of the teeth is faulty so he went back (the front half is missing). He was basically stone-walled by the shopkeeper who referred to wear and tear (it's clearly brand new). She is a bit scary. Any tips on how to make sure I get a replacement. TIA to anyone who might respond