Game Online Store's unprofessional behaviour

Purchased an item that advertised. The payment was made, the order was accepted and terms were delivery within 7 days. The advert continued to appear. When after 10 days I enquired about slow delivery the order was cancelled based on "no stock". The normal Game stores had stock. Don't they know when orders exceed the stock reserved for the 'special'? Does Game not consider the transaction concluded (a commitment) when they accept my payment and confirm the order? To add insult to injury they only reversed the payment about 14 days later, so they sat with my money for nearly a month.