Mistakes on the Royal Mail website have resulted in some customers paying double for postal services.
The company admitted to charging around 600 customers twice for postage costs at an average cost of £50 each time.
Problems occurred when people tried to pay for postage online and the website initially told them the payment had failed and asked them to re-enter their details, which resulted in their cards being charged twice.
There were also issues with customers paying for delivery online and these details not printing out onto envelopes, as well as customers topping up pre-pay accounts but the money not being shown on the website.
Other online services such as stamp buying and redelivery have also experienced problems.
Royal Mail is contacting those affected as a matter of urgency. If you've been charged double you will be given a full refund for anything extra you have paid plus a 'goodwill payment' of £25.
Royal Mail and Capgemini, which manages the Royal Mail website, issued a statement admitting to overcharging customers owing to the technical issues.
Moya Greene, chief executive of Royal Mail Group, and Paul Hermelin, chief executive of the Capgemini Group, issued the following statement: "We would like to apologise for the difficulties some Royal Mail customers are experiencing with a number of the applications on the website. We very much appreciate that this is the busiest trading period of the year for many of our customers."
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