A. Lee Graham Reporter Several customer services will be unavailable when the North Texas Tollway Authority upgrades its computer system. From 8 p.m. Friday Dec. 20 through 7 a.m. Thursday Dec. 26, ZipCash and TollTag account management and payment services will not be available. Those include online, telephone and in-person interactions at NTTA customer service centers, as well as at ACE Cash Express locations and regional TollTag partner locations. “We apologize for any inconvenience as we work to enhance our system for better customer service,” reads a portion of an agency news release. All tolls and transactions during the transition period will be processed beginning Dec. 26. Customers with ZipCash invoice due dates that fall during the system closure will not be assessed late or administrative fees if the invoice is paid by Dec. 30, according to the agency. More information is available at 972-818-NTTA (6882). lgraham@bizpress.net