non fulfillment of order

I recently purchased a pair of boots online which appeared to be in stock and for which my money was taken however i have now, a week later, received an email that the product is out of stock and that i would now be issued with a store credit

firstly as the items were on sale, it would mean that if i were to purchase the equivalent at Zando i would need to pay more than the current value. secondly i would prefer my money returned as i used a debit card upon payment and refuse to now purchase any further items from Zando.