I'm surprised they didn't suggest you return it SallyMc. There's some info on this page here:
http://uk.lizearle.com/returns-and-refunds
A few months ago I had a problem with the pump action of my exfoliator not working. It was still quite full but I was unable to get the product out of the dispenser. I went to the King's Road store and explained my difficulty to the sales assistant who then tried as well but to no avail. She asked me when I bought the item and I said I couldn't remember - it might have been from the store, but it could have been part of a TSV.
I gave her my details and she called up my records on the till and then she popped off and came back with a fresh bottle for me. I thought this was great customer service as I'm sure if I approached Boots/Superdrug with a similar issue and no receipt, I'd be sent off with a flea in my ear.
Maybe times are a-changing.