I know you're (understandably) angry, pro {pissedrightoff}, but as you posted another time, when you're not feeling great, your DD picks up on it.
Please, please, just have a cup of tea and a break from thinking about this issue.
ASDA has got to sort itself out, and come up with a credible response (hope they consider a generous amount of compensation in the form of cash, say 250 pounds) because you are not responsible for things going wrong with online ordering, and from the comments your bank make, it is either ASDA or whichever processing firm handling the transaction / request to check on the funds being available which has 'messed up' but the customer sure as heck isn't able to control it...
You were left without sufficient funds to place even a small order with ASDA because of their minimum of 25 pounds, and yes, they need to check what went wrong, so they can positively confirm what happened. Not sure they'd be given much credit for having only half an answer.
I hate what has happened to you, and while ASDA might think themselves well and truly whiter than white, it seems their procedures are fixed, and their response to a customer's complaint, somewhat offhand.
We've seen comments from a few who have relatives (or themselves) working at ASDA and acknowledging there are flaws.
I might get flamed, mrs pro for suggesting a need for calm, but if you do get a phone call, you just want to be able to talk calmly, and while everyone on MN (and lots, no doubt, elsewhere) are as angry as hell on your behalf (as I am, too), it helps not to be flustered and unable to get your points over clearly...
Loved a post not long ago:
A phone call to Mrs pissedrightoff, right now, would not go amiss. It would be A Good Idea.
As said phone call has not occurred before 12pm I shall now suggest a goodwill token of TWO years supply of nappies. A bunch of flowers. £200 worth of shopping. Her original order (payment waived).
That seems to sum up something on the lines of helping a customer, and if anyone at ASDA is unhappy at the cost, just cut one playing of a TV advert, and use the cash saved to compensate other customers. People are more likely to comment in a positive way if they know you are not just wanting money, but accept responsibility for your mistakes, too.
Incidentally, Radio 4, You and Yours had an interview with the boss of the Co-Op on Monday, some other supermarket next Monday, and no doubt ASDA will be involved in some other show. Perhaps those with complaints about their orders at ASDA can submit a brief note of their problems via the You and Yours page, and see how the programme and ASDA deal with complaints about poor customer service and these bank problems which cause so much grief to customers, who are, after all, wanting to buy food and other items...