So I bought 3 boxes of chocloates that were on 3 for 2. All the same type. Then at the checkout the deal didn't go through, I noticed as only bought a few things. I went to cs and after checking the problem was that the manufacturer changed the barcode on the product and one box had a different barcode.
Tesco then gave me all three boxes even though it wasn't really their fault. I did feel terribly guilty