In reply to Choss Weasel:
The jacket is not fit for purpose, and you are being fobbed off. If they won't help then write a letter to the local Trading Standards for advice.
I'd suggest that you actually name the shop due to their poor customer service so that other people can steer clear of them. Don't see why the mods would delete a bad recommendation when they allow positive recommendations from reputable suppliers.
If the shop won't help then ask for a customer service department to write a letter to and mention the manager's name of the shop.
Mention the Sale of Goods act as well.