Bad service

I bought sneakers at foot gear a few weeks ago, the sneakers are Puma. I started noticing that they are wearing off & got worried because a month hasn’t finished since I bought them. I went back to the store with the sneakers to report my query. The service I got was not up to the standard. I bought them using using my bank card, I had my bank statement with the proof of payment as I miss placed the slip but the answer I got was that I won’t be helped because I don’t have the slip. I’m so disappointed