Some 260,165 customers who travelled overseas were involved over a six-year period, ACMA said yesterday.
The penalty: ACMA said it had issued a "formal warning" to Telstra for having breached the Telecommunications Consumer Protection Code.
Defending the light penalty, ACMA said the incorrect bills reflected incorrect information Telstra had received from international carriers and its contracted data clearing house. But it noted Telstra had first received a complaint from a consumer who had been incorrectly billed in 2009. Billing inaccuracies after that were caused by Telstra's failure to investigate and identify the problems with the information being provided by its contractor, it said.
However once the information problem was discovered, Telstra promptly identified all customers who had been incorrectly charged and is providing rebates. It has also permanently ceased charging a flagfall fee for international roaming data services, ACMA noted.
"Accurate billing is of the utmost importance," ACMA chairman Chris Chapman said yesterday. "Our investigation makes it very clear that all telcos need to listen to their customers who report billing problems and be vigilant about any potential issues."
He said the decision to formally warn Telstra for the breach took into account that Telstra was not the original cause of the problem; that this was the first time a billing issue of this nature had been investigated under the TCP code; and that Telstra itself reported the matter to ACMA.