Optus did not escalate at least five calls that were made to its customer service centre, including two from NSW, that informed the telecommunications company that a technical error was preventing customers from calling triple zero.

CEO Stephen Rue this afternoon confirmed that Optus had found a further three calls, additional to the two announced yesterday, where customers had complained that they could not call triple zero.

Rue said the calls were not adequately escalated within Optus' system, meaning the telco was unaware of a major systemic failure until after 13 hours.

The inability to call triple zero affected South Australia, Western Australia and the Northern Territory between 12.30am and 1.30pm on Thursday.

A total of three deaths have thus far linked to the outage.

A fourt

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