An ACMA statement said Telstra's systems were configured to send SMS notifications about the usage - but these could not be received by broadband customers who were not connected through a mobile phone account.
ACMA chair Nerida O'Loughlin said Telstra had conveyed the fact that, between September 2013 and May 2019, it had breached its obligations under the Telecommunications Consumer Protections Code to inform customers about excess usage.
“Usage notifications give people due warning that they may be about to incur additional charges for their broadband services,” O’Loughlin said.
“Consumers have a right to make informed decisions about their broadband use, and by failing to send these notifications in the correct format people have had to pay excess usage charges without sufficient warning.”
The ACMA statement said Telstra had refunded all customers who complained and had incurred excess charge of $5 or less. All other affected customers had been advised they could claim a refund using an online form.
“We encourage current or former Telstra mobile broadband customers to contact Telstra for a refund if they believe they incurred excess usage charges as a result of not receiving a usage notification,” O’Loughlin said.
She said any further breaches were likely to result in more serious action.
“The ACMA has asked Telstra to report regularly on its progress of refunding affected customers until all customers have been reimbursed,” O’Loughlin added.