Bad Customer Service

I bought two packs of underwear of the same size as per the labeling on the packs. however the one pack is smaller than the other one and now they won't give me a refund or give a different pack. What do they expect me to do with smaller size when it's their labels that were incorrect.

This is bad customer service and I don't appreciate being treated the way i was by the security guard at the store in Maponya mall when he didnt even want me to see the manager or even get into the shop.