My son bought some brand-name trainers for £120, and after just three weeks the sole has come off one of them. I took them back to the shop but they say the manufacturer has a policy of not replacing them in these circumstances. I asked the shop to send them back to the manufacturer, but the shop doubted I would get a refund.
Assuming the fault occurred through normal wear and tear the shop must replace the trainers. Shoes that break after just three weeks are not of satisfactory quality, and your son can sue the shop for the return of his money if necessary. The manufacturer’s “policy” is no concern of yours. I suggest you contact your local Citizens Advice Bureau : they may take up the case for you.