Ethics and values?

I bought a pair of slippers in April, I noticed this morning that it tore on the seam. I took it back to PEP Lemon tree, the cashier referred me to Amy. I explained that I did not keep the slip as it was a perfect fit. Amy then advised that I can fetch a pair and if they break so easily that I should consider taking something else for the value. I took another pair of slippers & met her at the counter. She changed her story and said they couldn't exchange as I do not have a slip and the cashier will be short on her till ? Amy is so friendly but so lost when it comes to customer service and store procedures. Why agree to exchange wasting my time by making me choose another pair then change your mind? Then all of a sudden there is nothing she can do she will give me the regional managers e-mail address, then I ask her to write it down and she again changes the story and said that I should rather phone customer care myself and they will redirect me? It's really not worth it buying an item and after approximately 4 weeks I have to throw it away? I left the slippers at Lemon Tree as I am definitely not wearing those again! This went from maybe manufacturing fault to principal and ethics, changing stories so many times?