I ordered a product online which was at first confirmed but later on canceled by the online distributor due to lack of it. How to get justice?

On may 11th 2012 i pre ordered a product (Diablo 3 collectors edition) from an online store (walmart) which was due to come out on may 15th 2012. They told me the arival date for the product would be on may 24th 2012. During the time i was suposed to recieve another email confirming that the product has been shipped.Since I never reicieved such an email i contacted them 3 times to make sure that i will recieve the product. Twice through an email and once i called the customer hotline. They told me the product was fine and it was being processed for delivery and that i will recieve it by the schedualed delivery date. On may 22nd i recieve an email saying that they had ran out of the product that i ordered and are cancelling my order. I would have chose to shop at another online store but during the time the product had been sold out everywhere and the stores that still had the product it almost trippled in price. It rose from $100 which was the original price to $250 in time.What to do?