You can cancel your Citi credit card by phone or via your Citi online account.
If you want to cancel your Citi card by phone, call the bank representative at 800-950-5114. The representative will require you to provide your credit card details to close the card. However, the bank's representative will try to convince you to retain the card, and you may be forwarded to the customer retention department to try and persuade you against the decision.
If you prefer to cancel the credit card without calling the bank, log in to your account at citi.com using your assigned credentials. On the dashboard, scroll down and click “contact us” and then go to “chat with Citi”. Once a chat box pops up, ask the live chat support to cancel your credit card.