Got some headphones a few weeks ago and they are playing up. We have no box and no receipt. Also we bought them when buying other stuff so all we could find out is what date they were bought on (we don't usually use tesco)
Would you chance it trying to get a refund/replacement?
they are faulty, it's not that you just don't want them and have changed your mind. If it is a product that can be bought in other retailers they will probably only exchange them as you have no proof of purchase,
ummm you just need to give them the product and then the date and the last 4 digits of your card, ask them to check the back office system. they can print off a copy of your transaction. telling them which till you used would help but it's not always easy to remember in those big stores.