Company refusing to refund my money

I ordered a pair of shoes online, I got an email telling me they were out of stock and a few other suggestions, but I just want my money back. I emailed them and they''re refusing to refund me; even with the phrase "If you don¿t want to choose the alternative products and request a refund , we will refund the amount you paid immediately" in their Costumer Service section. What can I do?