Credit Card Customer Service Call: 866-820-3947 Credit Card Activation Call: 800-527-7728 Lost or Stolen Credit Card Call: 866-820-3947 Within the United States 24 hours a day, 7 days a week Call: 00 + 1 + 314-542-7111 Call collect from anywhere globally Credit Card Payment Mailing Address Mastercard® P.O. Box 71050 Charlotte, NC 28272-1050