What rights do I have if I've ordered something from a website and the Royal Mail has subsequently lost it?

I ordered a hoodie for my boyfriend for christmas from Hot Topic's EU website and it's now been over a month, been emailing the company who are basically blaming the Royal Mail but I'm being told that I can have a refund or a difference item if the item I ordered is out of stock (which it basically is). Do they not have a responsibility to get the item to me that I have ordered if they've taken the money for it? I don't want a refund, I just want my boyfriend's christmas present!