These types of computer issues always have happened. Often smaller sites have more of these types of issues although I have experienced them on sites such as Travelocity. The bigger issue is the customer service AFTER the problem. This is where the company totally failed.
They lost a customer and probably many more by not working with you to resolve the issue. I somewhat speculate that their people (person?) was tired from dealing with more than one problem but this is really no excuse. So often companies do not properly anticipate the response to a change, like a sale, and have great difficulty dealing with the volumn or problems.