Pick n Pay slips up on poor quality slippers

I bought a pair of slippers at William Nicol. After wearing them for four days the soles started to crack and peel. I took them back to PNP Norwood Hyper as my nearest branch as quickly as possible showing the date on the slip. The manager admitted that these same slippers were part of the stock at Norwood, but said she could not give me a refund because they had never had a return on that particular stock. I pointed out that PNP is a national company and that it should not make a difference, Stock is stock. She said I would have to go back to the William Nicol branch - that would cost me more in petrol than the cost of the slippers. I am now stuck with ruined slippers that I cannot wear.