Poor and bad service from security and manager at matlapeng freedom park

Went to pep store in matlapeng in devland freedom park, I bought pyjamas size xs but when I arrived at home I realised top n bottom not same size top is xs that I want and bottom medium which big for me when I go back to do exchange is where I realise I forget slip back home and I explain to security at the ma problem bt I left slip back home he told me that won't happen since I don't have slip so demanded to see store manager store manager the told Me must go to nearest bank do to statement so they can make sure I bought the item there, so ma questions is why they don't want to swap bottom for me because it's they're mistake at the same time to Merchandise/put pyjamas that are not same sizes at the first place now I sitting with pyjamas that are not fitting me