Refused to change shoes

I purchased a pair of shoes. When I tried it in the store it was fitting. When I used it to go out then the left leg seems a little loose. I took it now to Woolies in Sandton and the manager Xolani Simelanie says he wish he could refund me but I used. Obviously I would have used it to know the difference. Why can't I get another pair of shoes. I'm not asking for a refund