Noticing Unauthorized Transactions
Before you can dispute an unauthorized withdrawal, you must first notice that the withdrawal took place. The Internet allows you to log into your account at any moment and view your log of transactions, even those that haven't cleared the bank yet. You can also set up e-mail or text message alerts to let you know your balance; if you notice a big discrepancy from one day to the next, it might be a sign that something's wrong with your account.
Notifying Your Bank
The first thing you should do if you notice irregular activity in your account is contact your bank immediately. You can call the customer service number on the back of your debit card or locate the fraud hot line on your bank's website. Most banks advertise that you'll have only limited liability for unauthorized transactions; if you report the transaction within 48 hours, your liability is limited to $50 in many cases. However, if you wait until after that time frame, you can be held liable for up to $500.
Filing a Dispute
After you've called the bank, it's up to you to try and recover your money -- if the situation allows you to do so. If you lost your debit card and someone else used it to make purchases, the bank will replace the money in your account shortly after you contact them. But if the unauthorized withdrawal was the result of a billing error, such as a recurring monthly fee for a service you canceled, you will have to contact the billing company directly to rectify the issue, which can be a lengthy process. Even if the billing company acknowledges its error immediately, you'll likely have to wait at least a few days for a refund.
After the Dispute
Once you've notified the bank and the party that performed the unauthorized withdrawal, stay on top of things until you have your money back. If the unauthorized transaction was the error of a third party, make sure to hold the party to any refund time they have quoted you. Once you've been reimbursed, you can call your bank and ask personnel to reverse any overdraft fees you may have been charged as a result of the unauthorized transaction.