If you just processed a transaction using your debit card and it is still pending, you must then wait a day or more before it finalises. If for one reason or another you changed your mind about the charge and no longer want the item you purchased, you may wonder if the bank can just cancel it while pending.
A pending transaction, also called an authorisation hold, is an amount deducted from an account holder's balance but not yet transmitted to the merchant. For a debit card, the bank withholds the amount from the consumer's current account balance. While pending, both the account holder's bank and the merchant's bank communicate with each other to finalise the transaction. It commonly takes between one to five business days.
If you call your bank to attempt to cancel a pending transaction, it is unlikely that the representative will be able to comply. In most cases, once the transaction is pending it must post to the account before any additional action is possible. The only situation where you might be able to have a pending transaction dropped from an account is if it is an accidental duplicate transaction -- two charges of the same exact amount at the same time.
Instead of attempting to cancel a pending transaction you must contact the merchant to request a refund. The merchant can then send a request to his own bank to have the transaction reversed after it posts to the account. If the merchant does not agree to a refund and you feel you have a justifiable reason for a refund, such as an undelivered item or an item erroneously described, you can dispute the charge with your bank after it posts to cancel the purchase.
Keep in mind that when you dispute a debit card transaction it causes a "chargeback" to the merchant. The merchant must pay expensive fees for this situation and may be able to place your debit card on a blacklist to prevent future orders. For this reason, you should always attempt to resolve the situation with the merchant directly before taking action with the bank.