Contact your bank as soon as possible, within 60 days of the transaction at the most. You may be required to submit the alleged error in writing. Banks typically investigate the error within 10 days. Your funds should be reimbursed if the bank can’t find an explanation for the alleged error. In certain circumstances, such as a point-of-service debit withdrawal, the bank may be allowed more time to investigate the error.
The bank should notify you of their findings in writing, regardless of whether they found an error. If there was an error, they must finalize your reimbursement.