Thousands of Kent Co-op customers may have potentially been charged twice in a blunder involving the food giant's petrol stations and food stores.
It's not known how many customers UK-wide might have been affected by the error on Tuesday, but it could run into the hundreds of thousands.
Those affected will have their money credited directly back to their accounts within the next 24 hours, the retail chain has said.
It has also promised to reimburse people who have incurred charges as a result of the error, such as overdraft fees.
Among those affected was Chatham woman Elizabeth Bugden, who said she was charged £120 when she spent £60 at the Co-op branch in Rochester.
She said: "I shopped it the Co-op in City Way on Tuesday. I've checked my bank today and they had taken double.
"I've tried to contact them. They just keep saying they're sorry and they are trying to get it sorted. They reckon it was an IT problem."
Another customer, from Higham, spent £71.95 at the Co-op store on the Medway City Estate on Tuesday, and was also charged twice.
"We would like to apologise to all those affected" - Co-op spokesman
She says the money is yet to be put back into her account.
A spokesman for the Co-op said the mistake was down to a "processing error".
A statement for the Co-operative Food said: "Due to a processing error customers who shopped with us or used a petrol filling station on July 7 using a credit or debit card were charged twice.
"We would like to apologise to all those affected, and reassure customers that refunds will be made directly in to their accounts within 24 hours.
"We will also reimburse any customers who have incurred bank charges as a result of this error.
"These customers should contact our customer careline."
Have you been one of those affected by the Co-op blunder? Email us at firstname.lastname@example.org