Casa Dolce and Gabbana

Good day, I have purchased the gown at Casa Dolce and Gabbana, so when I get home I realised it doesn’t fit me well it’s too long on my hands and it’s how it designed, so I communicated with the sale personally to changed the item with the D&G sneakers, then he told me it’s not the same shop and he continued saying hence he told me it’s two different shops ( which when he explained he said inside they deal with clothes outside it’s is the things for the house but never explain that they not working together which when I paid we went inside the D&G shop) the tricky part i do not want anything else on theirs shops, I only liked gowns i even told the sales person, so now they only give credit which I'm force to take something at their shop which he never explained that before I pay, when I ask of why there was no explanation he said the explanation is at the back of my purchase slip so the explanation it come after I have paid I’m so disappointed.