I agree that contacting them concerning the issue is in order and probably more importantly being disappointed that you may not have been notified about the stock shortfall after you had placed the order... but there are very valid reasons that are beyond their control that cause this type of thing to happen ( the stock shortage that is ).
The stock levels shown in web based store software can not be 100% accurate... the stock levels aren't in "real time" like those done on a computer in a store... they are dependant on who and when the browser loads the item and then again when the checkout is finished.
A good example of this is seen even on forums... how many times have you made a post right after someone else only to find there are other posts made just before your own, many times they can be listed several posts later even. So a handful of posts made at the same time... someone will always be posted last. The same happens with shopping carts when there may only be one of the product left.
Errors in stock levels also happen quite often even in real time softwares but are more likely in web based ones. A person that is pulling the order can grab the wrong product or the person pulling an item for an RMA replacement may not do their "paperwork" until after ensuring the product is in stock and pulling the item. Stock levels in small business's will often only be audited once a month so the errors in stock levels can be there for a relatively long time in some cases.
In the end, when this type of thing happens... we only have a valid complaint when we aren't advised of the error promptly and given a choice of waiting, selecting another product or getting a refund.
