Dis-Chem poor service

We bought replacements brushes for our tooth brushes. Once we opened the packet, ee realized they do not fit. When we try to exchange them, Dischem refused, because we've open the package. How must we know if we do not open the package? There was no discussion - just no, you opend the package, so no exchange. Be carefull, they catch you without assistance in the shop. Poor, poor service. I'll go to Clicks rather.