Lost or Stolen Cards. For your convenience and the security of your debit card, contact Citizens National Bank at during business hours. After. Free Mastercard debit card accepted around the globe and online; Use your debit deposits at CNB ATMs; Register your card with Mastercard SecureCode for. Lost/Stolen or Blocked Debit Card The number for a customer to call after regular banking hours for a lost or stolen Master Card Debit card is For​.