Unreliable shop

I bought Brooks glycerin gts running shoe end of March 2025 and I ran a marathon with it. I had a discomfort that I've never experienced for past 3 years running with this type of shoe. It's only the latest of it that gave me problems . I reported it to SportSA and they told me that they can't refund me as the shoe does not have a problem and maybe its not suitable running for me. They said they'll give discount if I buy another with them. They don't don't want to admit that the running shoe has got a cushioning problem.