Telstra overcharged thousands of customers almost $2.5 million over a 12-year period, the telecommunications watchdog says.
The Australian Communications and Media Authority ordered the giant telco to lift its game and comply with federal billing accuracy laws.
Investigators found more than 10,000 customers were fleeced about $231 on average between February 2008 and February 2020.
Most were being provided an interim Telstra service at the time - usually a mobile phone - due to delays connecting or repairing their landlines.
ACMA chair Nerida O'Loughlin said the errors were a clear breach of the Telecommunications Consumer Protections Code.
"For Telstra to allow an issue like this to go unnoticed for such a long time and impact so many customers, is simply unacceptable," she said on Thursday.
Ms O'Loughlin said customers shouldn't be charged more for interim services than they ordinarily would have paid under their existing or requested landline service.
"Overcharging can potentially lead to financial difficulties for affected customers which is why the ACMA considers accuracy in billing practices to be an important consumer protection," she said.
Telstra self-reported the overcharging breach to the ACMA earlier this year.
It says the billing error resulted from IT mistakes when a new customer database was launched in 2008.
"Getting something as important as billing wrong isn't acceptable and we apologise to our customers," a spokesman for the company said in a statement.
"Since we discovered the mistake we have been working to refund customers and change our processes so this can't happen again."
ACMA formally directed Telstra to comply with the TCP Code, warning any further breaches could lead to a fine of up to $250,000.
Australian Associated Press
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