returning an item

On Friday evening I purchased a sling back high which fit perfectly.had it on Saturday for a few hours and during the walking process of the day the sling jammed into my tended which knowing they give my money as I wore it I called the store and enquired could I swop it for a size up as I love the shoe the manager who was sweet says no they will be putting the shoe back onto the floor and because I wore it I t won't sell.i said to him I understand but can't it be sent back to the factory as I cannot wear the shoe, what can I do?He politely says I don't know. So now I'm sitting with a shoe that I cannot wear. Very upsetting.