Document your reasons for needing to block your ATM card. If you are afraid that someone has obtained your personal information, write down exactly when and how you feel they obtained it. If you left your card somewhere, write down where you left it, along with the date and time. If there are any suspicious charges to your account, make sure to note those as well.
Set aside some cash to use in case you cannot access your bank account for a few days while the bank investigates what is going on with your ATM card. If you have other accounts, you may be able to use those while the bank conducts its investigation. Otherwise, it is always smart to have enough cash on hand to cover necessities for a few days.
Call your bank and share your documentation with them. They may ask you additional information about the security of your account. At this time, they will block your ATM card and may even issue you a new bank account number. You may be unable to access your account until they mail your new information and ATM card to you.
Activate your new ATM card when it comes in the mail. Usually, a toll-free number will be listed on the card. You will need to call the number, give the customer service agent some personal information, and then your new ATM card will be activated for use.
Take proper security precautions in using your new ATM card so that you do not have to have it blocked again. Check your bank balances daily and be selective about where you use your card, especially on the internet. Consider using an identification theft protection service to protect your account from further harm. You may also consider using a service that gives you a unique card number every time you order with your ATM card on the Internet. The unique number will only work once and will help to keep your finances safe in the long run.