If your checks or debit card are lost or stolen, please report it immediately to Cornerstone Bank at 701-364-9630 or 888-297-2100. To report a lost or stolen debit card after hours, please call 800-472-3272. To activate or change your PIN, please call 800-992-3808. If you have MasterCard questions while traveling, please call 877-253-8964. If you have questions about your MasterCard benefits, please call 1-800-MASTERCARD (1-800-627-8372). Click here for debit card FAQ.