TPG Telecom chief executive Inaki Berroeta on Tuesday said his company discovered another customer was unable to call triple zero because their phone was not compatible with the 4G emergency network.
The person got through by alternate means five minutes later but is believed to have died on September 24, which TPG claims it only learned of on Monday night.
Communications department representatives were caught off-guard by the revelation, having been told by TPG on September 26 there was no death linked to the incident.
Telstra chief Vicki Brady told the same inquiry her organisation knew about the death the day it happened, while no telco or government has told a series of public hearings in the months since about the incident.
Communications department first assistant secretary Sam Grunhard said he learned of the incident on September 24 and promptly told the office of Communications Minister Anika Wells.
But two days later, TPG incorrectly told the department there was no death.
"Everyone in the department and the minister's office were very relieved to learn that, in fact, there was no fatality associated with this incident," Mr Grunhard told the inquiry.
Senators were appalled the department had not shared details about the incident and not probed what had happened with the TPG issue.
"Laissez-faire is exactly what's coming across," Nationals senator Ross Cadell said.
"You're saying 'we got this call and we thought it was another outage, but then it was just a handset issue' … no, someone had died with the information you had."
Despite intense publicity surrounding three deaths linked to a major Optus outage on September 18, the TPG-linked death six days later was not addressed publicly until the hearing on Tuesday.
Ms Brady said Telstra had never raised the death in meetings with Ms Wells, or at a roundtable of telco chiefs in October.
Greens senator Sarah Hanson-Young said she was "flabbergasted" no one within the industry declared someone else had died.
"Not at one point in this did anyone within the industry want to fess up and say there'd been another death six days later," she said.
"It's a cover-up. You're all looking after yourselves."
The person lived in Wentworth Falls in the NSW Blue Mountains, although TPG was yet to confirm details of the incident with emergency services and could not provide further details to the inquiry.
Ms Wells was in New York promoting a social media ban at the time of the death.
Investigations are underway into what happened and why the department and the communications watchdog weren't provided the correct details, a federal government spokesperson said.
"It is disturbing to hear about this tragic outcome," the spokesperson said.
It is the second death linked to services from TPG, which also operates the Vodafone and Lebara brands in Australia, after a customer failed to reach triple zero on November 13.
Early investigations into TPG's November incident pointed to the customer's ageing Samsung phone using software incompatible with making triple-zero calls.
TPG has said it made regulators aware of the problem at the end of 2023 before the national 3G network shutdown.
Under Australian laws, telcos are required to block devices if they are unable to call triple zero.
Samsung mobile division head Eric Chou said about 98,000 devices needed a software update to be able to access triple zero.
Samsung has identified 11 models needing replacement and another 60 requiring a software update to overcome the 3G network issue.
The issue with the Vodafone network, affecting Samsung, Apple and Huawei devices, was discovered by Telstra and Optus in late-October, a year after the two telcos turned off 3G.
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