Zando bad shopping experience

I ordered an item from Zando and wanted to exchange it. I could however not returned the item because their system showed that the item was not delivered yet even though I received it the previous day. They then blamed DSV the courier company. I phone DSV and they confirmed that their system correctly showed that the item was delivered. Zando also informed me that they do not exchange item, they only refund. I have to re-order. I though online shopping was supposed to be convenient. All I wanted was to exchange the item for a differed size. With this kind of service I'll think twice before ordering from Zando again. Their customer service centre also refused to let me speak to upper management