If you are having trouble making an online payment or need to reach Walmart credit card customer service for another reason, the phone number to call is 1-877-294-7880 for the store card and 1-866-611-1148 for the Walmart MasterCard.f you want to send in your Walmart credit card payment, here is the mailing address: Walmart Credit Card. P.O. Box 530927. Atlanta, GA 30353-0927. or, if you want to send a payment via overnight mail: 485 Lake Mirror Road. Building 700.