Bought 3 beauty products online on a 3 for 2 offer. Two are the same product. Used one last week and had an allergic reaction. Have contacted the company who have apologised but are only prepared to refund the unused item as the one I used was technically free. Are they correct? I would be happy to swap for something else but they are refusing. But I feel I have lost the “opportunity cost” of that third item, if nothing else. How does this work?