Telstra was hit with a formal warning for failing to notify some mobile broadband customers by email before they used up their monthly data allotments.

The Australian Communications and Media authority (ACMA) said the operator didn’t send email alerts to more than 150,000 customers, who were charged for unexpected excess usage, due the its systems being set to send SMS notifications, which some customers were unable to receive.

Telstra reported to ACMA it breached obligations to email notifications to customers between September 2013 and May 2019 .

ACMA chair Nerida O’Loughlin said usage notifications give people due warning they may be about to incur additional charges for their broadband services.

The country’s Telecommunications Consumer Protections code requires service providers to email customers within 48 hours of them reaching specified data usage quotas on post-paid plans.

Telstra said it refunded all customers who lodged a complaint and also contacted other affected customers, who can claim a refund via an online form.

O’Loughlin noted further breaches would likely result in more serious regulatory action and asked Telstra to report regularly on its progress of refunding affected customers until all have been reimbursed.