Shoes labelled as wrong size

Bought a pair of Grendha shoes labelled as a size 8. The printed shoe city sticker labelled as size 8, the shoe city hanger labelled as a size 8. Turns out it was a USA size 8 which is a SA size 6. I wore them for a short outing on a Sunday, they felt a little tight they were sandals but I gave them the benefit of the doubt. I cut my outing short and went home I was in so much pain. Got home decided to look at the shoes a little closer. 3 sizes shown on the bottom, none of them ones we use in SA. USA 8, EU 39, AU 37. The staff don't understand the huge difference between a USA AND UK size and won't take them back as I wore them. Beware of shoe labels at shoe city.