AUSTIN, Texas — A printing issue caused Austin Energy to send duplicate utility bills to more than 12,000 customers, but the error will not result in any charges, officials said.

A total of 12,638 customers received two bills due to the error, which occurred during a billing system upgrade, according to Austin Energy spokesman Matt Mitchell.

The utility immediately contacted affected customers to explain the situation and assure them their accounts and payments remain secure.

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Customers can verify their correct account balance by logging in at COAUtilities.com, calling 512-494-9400 to use the interactive voice response system or speaking with a customer service representative at the same number.

If a customer pays the incorrect bill, any overpayment will automatically be credited to their next statement or can be refunded, Mitchell said.

Customers who receive e-bills or are enrolled in AutoPay were not affected.

Austin Energy is working with its vendors to determine the cause of what Mitchell described as a “highly unusual and isolated” incident.