Refused to do an exchange

I bought sandals for my daughter last week Thursday at Pep Hayfields mall, Pietermaritzburg sadly when I got home they didn't fit her. So I went in today to try and exchange for a correct size sadly again I seem to have misplaced the till slip. I was told they can't help me without a slip. I must go find a slip and come back with it soo disappointed surely there is away of doing an exchange, I wasn't asking for a refund just wanted to change sizes. Surely they can scan the product .