Bad customer service

I bought some kids toys on Saturday and my son opened the box that evening only to find out that the arm for the Legq was missing so I told him to put everything back and we will change it tomorrow morning(Sunday). We went back to the store to exchange and the sales assistant refused to exchange even though I produced the till slip. There was no manager in the store and he said I must call his boss in China. Although this was only 15 bucks but the manner in which i was received was horrible. Makes me wonder how people can get ****** over the festive season!