The Optus cyber attack is being blamed for a jump in the number of complaints about telecommunications companies.
Complaints from small businesses and households rose 9.9 per cent from October to December, according to the Telecommunications Industry Ombudsman.
About half of the 17,903 complaints related to mobile services, which is an increase of about 19 per cent.
Complaints about internet services jumped by more than 10 per cent at the end of 2022 but dropped by more than 20 per cent for landlines.
More than 10 million people were caught up in the Optus data breach, when cyber criminals stole identifying information such as names, contact details, Medicare records and passport data.
Many mobile customers reported non-financial losses including stress and humiliation in the months following the hack.
Telecommunications Industry Ombudsman Cynthia Gebert said there were also concerns about termination fees, customer service and failing to cancel a mobile service.
"The complaints from this period of October to December really highlight the problems people are experiencing because of this breach," Ms Gebert said.
She added her office was working with Optus to ensure consistent approaches were being taken when resolving concerns.
The number of complaints about Optus rose by more than 39 per cent and increase by almost 21 per cent for iiNet.
Complaints about TPG and Vodafone also increased but dropped for 10 other major telcos.
Meanwhile, Telstra has vowed to fix problems with a system designed to ensure customers with life-threatening medical conditions receive extra assistance.
The telco is required to provide the service as a condition of its carrier licence.
A probe by the Australian Communications and Media Authority found Telstra failed to send applications for the program or other relevant information to 260 customers.
It also failed to initiate emergency medical request procedures on five occasions and did not follow proper testing protocols for one customer who had repeated issues.
The company admitted it could not find paperwork relevant to applications on more than 700 occasions.
The telco could be taken to court if it fails to implement a new system.
