Unfair return policy

I bought a pair of stockings at the woolworths store at King Shaka International Airport on the 26th May. I then realized that the stockings wouldn't fit when I had opened the packing. When I tried returning the stockings I was told that because I had opened the packing I was no longer eligible for an exchange. First the lady Thandazile Ndimande asked for a slip then I explained I didn't have it with me but they could reprint as I had bought the stockings there. Next she advised that the packing had been opened therefore I cannot exchange the item.