Pep disappointment

I had a very bad experience at Pep Store Mamelodi Denneboom. I bought clothes for my son only to find that the clothes are smaller on him, I went back to the store for exchange and I was told that I do not have the correct slip for my request, the slip that I'm having is the wrong one only to find that the very same slip they are talking about it's a store copy which was supposed to be in store. The cashier erroneously gave me the store copy and kept the slip which was supposed to be mine in store and now the store tells me that there is nothing they can do, they won't even be able to trace my transaction on their system so that I can get the correct slip now I have to stuck with the items that I won't be able to use because of their own mistake...I'm very disappointed in Pep