Once an order has been submitted it may not be possible to cancel it as some orders go straight into production. 

However, in other cases there is an option to cancel orders on the Prodigi account dashboard. If the option is available to press then orders can be cancelled. 

Please try this option first and if the option isn't there contact support us as soon as possible - if the order has not yet been processed by the printer we may be able to stop it for you.