Asda customers who shopped online this month have been overcharged for their groceries, with one claiming to have been charged nearly five times the correct amount, following a computer glitch.
A power cut at the supermarket's US servers on August 16 caused a temporary problem on the home delivery website, Asda confirmed today.
A spokeswoman said because many customers order their shopping in advance, the overcharging problem first came to light this week.
The glitch was fixed on the day but shoppers have complained of being left short on cash as Asda worked to correct the problem and offer refunds.
Asda apologised to customers, promised to refund the their money, any resulting bank charges and their original shopping bill as a goodwill gesture.
Some customers have received their money today, the spokeswoman said.
But while some shoppers waited for money to reach their accounts they complained of not being able to feed their families or fill their cars up.
Customers posted comments on the website of consumer watchdog Which? about how they were affected by the glitch.
One, named only as Paula, said: "My shopping came to £50.96 - they took £250 out of my account. I'm now unable to access this week's wages as it will take up to five days to go back in my account. They have offered compensation but how do I feed my family for five days?"
Another, Katrina, said: "The only way I knew it had been taken out was that my husband filled his car with fuel then his card was declined. He had to call work and borrow the money."
An Asda spokeswoman said: "A power cut at our computer servers in the US has resulted in a temporary system error on the home delivery website.
"As soon as we became aware of the overcharging issue we contacted the customers affected and refunded the overcharge and any resulting bank charges. Some customers have seen the money hit their accounts today, and we're confident all customers will have refund in the next couple of days at the latest.
"Our initial investigation has shown that this was an isolated incident, but steps have been put in place to make doubly sure it doesn't happen again. As a gesture of goodwill and to say sorry our mistake, as well as refunding the overcharge we have also credited our customers' accounts with the cost of their original shopping order.
"We apologise to our customers that have been affected by this technical glitch.
"As far as we know it's nothing to do with Hurricane Issac - our servers are in Arkansas."