shop doesn't have size and don't want to refund me

I went to Side Step in Boulders Mall yesterday (16/01/2016) to buy a sneaker (Rhapsody Sneaker) and I was convinced by a sales consultant who didn't have a name badge that it was a Ladies Sneaker all to find that they **** to me it's a guys sneaker. When i arrived home i found that they have given me a wrong size which is size 5 for men of which it was very big. I went back to the store the following day to do an exchange at least to size 4 and they told me that they don't carry size 4 at their shop. I asked for My refund back and sales consultant with bad attitude who refused to give me his name told me that it's not a shop's fault that they don't have a size that I am looking for because they never asked me to come to their shop to buy a sneaker and they will not refund me. I am now stuck with a sneaker that I have paid for and will never wear it as it is not my size. All i need is my refund back.