Sitting with a jeans that doesn't fit

Good Day I had purchased a pair of jeans towards the end of August from their Southgate branch. When I went back to change it to a bigger size they advised that they can't help me because I don't have a slip... This confused me because I normally change sizes with just the tag. They then advised me that they don't change with the tag because of looting. I then suggested that they do a reprint or I could give them a proof of purchase via my banking app as I had paid with my bank card. The staff then laughed at me and gave me sarcastic remarks then ignored me and went about their business. I then called customer care where I also never got a solution or some sort of assistance... Bad service and still sitting with a jeans that doesn't fit.