When you go to check out at the store, the last thing you want to hear is that your Visa credit card is denied. It may not be that you have no available credit on the account but that the card is locked for some reason. Before you panic, take steps to unlock the credit card.
Call the bank that issued you the credit card. Visa doesn't keep information related to your credit account, so only your bank will be able to help you. The bank's phone number should be on the back on the card, but Visa also provides a list of issuing banks on its website.
Press the menu option relating to credit cards, then the option related to account questions. Bypass the menu choices to get to a live person if you prefer.
Explain to the representative that you can't use your credit card. It's standard procedure for him to ask you to answer security questions before he gives you information about your account, so be prepared to provide a phone password, address or phone number before explaining the problem. The representative will explain why the bank has locked your Visa card, as well as anything you need to do before he unlocks it.