In the case of orders that have been placed, but do not appear to be acknowledged, you must contact IBKR via telephone immediately.  We will need to contact the exchange in these cases.  Communication through web tickets is not real time, and can not be used for issues of an urgent nature.  Requests for trade cancellations/fills must be made within the time limits set by the relevant exchange.  Many equity exchanges have a notification period of 30 minutes or less.  Derivative exchanges have notification periods as short as 5 minutes.  Requests for trade cancellations should be made by telephone or the Bust Request tool (no email or other non real-time method) to IBKR within 15 minutes of the erroneous transaction.  IBKR requires sufficient time to prepare the necessary information required by the exchanges and this time is included in the exchange-specified reporting period.  Requests for cancellation are always handled on a best-efforts basis and IBKR cannot guarantee the reporting time requirements.  In addition, exchanges have bust request fees that account holders must agree to before IBKR can proceed with the request.  The fees vary by exchange, and you will be informed of what that fee is for the exchange in question prior to the bust request filing.