I worked in a bank and delt with ATMs. You have to report the incident to your own branch, it may be the case that the money came out and has automatically been relogged to your account, if not and you have been debted, your branch will than contact the branch that the ATM belongs to. The ATM will then be balanced (this is done every week) it should be over by the amount you tried to withdraw. It can take a few weeks for your account to be rectified