Obtain documentation to show as evidence that your debit card was overcharged. This can be a transaction number or receipt number. The transaction number can be located on your bank statement. Most banks allow online access to your statement, which is quicker than waiting for a paper statement or calling your bank to get a transaction number.
Contact the company that overcharged your debit card.
Explain to the company representative that you were overcharged. Tell him how much you were overcharged and provide a transaction number or receipt number.
Ask the company representative how long you must wait before the money is credited back to your debit card. The company representative probably will give an estimated time of resolution. This will give the company enough time to investigate the matter to ensure that you were overcharged. Be sure to document the name of the company representative you spoke with and the date you spoke with her in case you need to refer to it later. Monitor your account to ensure that your account is credited within the estimated time of resolution.
Contact your bank and advise a representative that you were overcharged on your debit card. This should be done as soon as you realize that you were overcharged. If your bank can catch the error before payment is actually made to the company, it may be able to put a "Stop Payment" on the transaction. However, this will vary by bank. If the bank is able to stop payment, there may or may not be a "Stop Payment" charge assessed to your account.