Customer having to correct the store's error

I made a purchase on the Mr Price online store. I received my purchase and they had sent me the incorrect size. I reached out to customer service and they tell me I have to return it to a store in order to get the correct size. How is this fair. I paid a delivery fee and they had got my order wrong and now it's my responsibility to correct it, how does this make any sense. The whole point of online shopping is so that we can stay safe and don't have to go to the store, this just defeats the purpose as well as its unfair.