Telstra has begun issuing refunds of about $30 million after admitting it had been over-charging customers for global roaming services on mobile phones since 2006.
The telco has been writing to customers for the past month informing them that their data charges while they were travelling overseas had been "incorrectly calculated" and they would be given refunds.
Despite the over-charging going back to 2006 and involving tens of millions of dollars, Telstra only became aware of the issue when it conducted an audit earlier this year. It is understood the issue only affected Telstra but a spokesman for the telco blamed international carriers.
"Telstra became aware of an issue whereby some customers were charged multiple data session fees due to the way international carriers generate their data usage records," the Telstra spokesman said.
"Once we identified the issue, we put immediate steps in place to prevent further multiple charging."
Regulators including the Australian Communications and Media Authority (ACMA) and the Australian Competition and Consumer Commission (ACCC) were involved in securing refunds for affected customers.
Elise Davidson of the Australian Communciations Consumer Action Network (ACCAN) said the challenge for Telstra would be getting in touch with ex-customers who are entitled to a refund but who are no longer with the provider.
"It is surprising that the inaccurate charging was undetected for six years and staggering to think of the number of bills Telstra will have had to review in order to provide refunds to consumer and business customers." she said.
"All telecommunications customers need to be able to trust that their provider is billing them correctly."
International carriers send data files to Telstra via a data clearing house for billing, and sometimes the carriers cut long data sessions into segments. The data files passed from the carriers have an indicator for when a data file relates to a part data session or a full data session.
It is understood that some carriers left the indicator for a part data session blank and that was interpreted by Telstra as a full data session, resulting in the data session fee being applied multiple times for a single data session.
Global roaming costs for Australians are some of the highest in the world and the Telecommunications Industry Ombudsman reported this month that complaints about disputed roaming charges increased by almost 70 per cent in 2011-12 to more than 4100.
The same day the complaint figures were released, ACMA issued a new draft international mobile roaming standard that would force telcos to warn consumers of exact charges while they are roaming and provide tools to monitor and manage their usage.
"We want the carriers to significantly lift their game on the whole transparency piece to give the consumers clear messages at the right time and the right warnings about costs, and then also to give them the tools they need to actually manage those costs," ACMA member Chris Cheah told Fairfax at the time.
"We don't think it's that hard and they should be able to do it."
Communications Minister Stephen Conroy said Australian consumers were being "gouged" by telcos and slugged with "unacceptable", "outrageous" charges.
The complaints to the Telecommunications Industry Ombudsman included a consumer who bought a $129 monthly plan so she could make calls during a nine-week holiday in Europe, only to return to a bill of $75,000 bill, which subsequently increased to $147,908.
Another consumer, while on holiday in South Africa, thought his mobile phone was connected to the hotel's Wi-Fi, so he used it to connect a laptop to the internet, but ended up with a $38,000 bill.
Mobile roaming complaints to the Ombudsman, Simon Cohen, represented about $8 million in disputed charges over the past 15 months and Mr Cohen said consumers were not being fully informed about the potential for extremely high charges and how they could protect themselves.
The Australian Communications and Media Authority said an investigation was underway into whether Telstra had breached the billing provisions of the Telecommunications Consumer Protection Codes.
"The ACMA is working with the Australian Competition and Consumer Commission and Telstra to ensure an appropriate outcome for all affected customers, including possible refunds," it said in a statement.
"As this is a current investigation the ACMA will not be making further comment."