Bad service at Dunns Store

Hi, I bought a jacket on lay buy from Dunns Mafeteng, Lesotho. In less than a month, I paid it up. Unfortunately it didn't fit my sister whom I bought it for. The very same day I went back to the store to exchange it, but I was denied the service and told that clothes bought on lay but cannot be exchanged. I read the lay buy contract conditions and nowhere does it say this. It only says cosmetics, jewelry and underwear cannot be exchanged. Please help.