Optus says at least 2697 calls were unable to reach triple zero during an outage that left millions of Australians without access to the internet or cell service.
The updated figures are a more than tenfold increase in the number of calls the telco initially reported from the outage on November 8.
The revised numbers were a "deeply concerning development" given the critical importance of the emergency service, Communications Minister Michelle Rowland said.
"Today, Optus advised the government that information it previously provided to the Australian Communications and Media Authority, the Senate and the public about the number of unsuccessful triple-zero calls from mobiles during its nationwide outage on 8 November 2023 was not accurate," she said on Tuesday.
More than 10 million Optus customers were without phone and internet access for up to 14 hours on November 8.
The telco blamed a software upgrade for the network breakdown, while the fallout triggered the resignation of Optus chief executive Kelly Bayer Rosmarin.
Optus previously disclosed that only 229 calls from mobiles to triple-zero did not reach the Emergency Call Person (Telstra).
The telco said a recent review revealed an additional 2468 customers made unsuccessful triple zero calls from the network.
Optus interim CEO Michael Venter said the company was apologising to affected customers.
"Regrettably on 8 November we did not meet the standards our customers and the community expects from us," he said.
The new information will be considered by the Australian Communications and Media Authority as part of its independent investigation into Optus' compliance with rules on emergency calls.
The rules cover obligations such as conducting welfare checks on people making unsuccessful emergency calls during an outage and providing access to emergency call services.
Compensation for impacted customers and ensuring confidence in the triple zero system will also be explored in the federal probe.
Ms Rowland said Optus would begin contacting affected customers.
