ACMA Chair Nerida O’Loughlin said four related ACMA investigations found 1,586 breaches by the telcos due to their failure to supply any replacement services.

“Many Australians rely on phone and Internet services for their work and home lives, and significant disruptions can have a heavy impact on their livelihoodsand wellbeing,” O’Loughlin said.

“TPG, Optus, Dodo and Telstra have all let down these customers and effectively left them high and dry during the NBN migration.”

Rules put in place by the ACMA stipulate that a telco must supply a replacement service after three working days of a customer being left without a service during a failed attempt to connect to the NBN.

Additional rules require that, if after 20 working days the NBN connection is still not working, the telco must develop a remedial plan to address the issue - and if the service is still not working after 40 working days, the telco must conduct a technical audit to identify the necessary steps to complete the migration.

ACMA says its investigation found that these steps were also not being taken by the telcos, with 5,158 breaches of the rules due to remedial plans and technical audits not being undertaken by the providers

Now all four companies have provided court-enforceable undertakings to introduce measures to improve compliance with the service continuity rules, and they must report back to the ACMA each quarter for 12 months.

And if the telcos do not comply with the enforceable undertakings, the ACMA can start proceedings against them in the Federal Court.

The ACMA says the success of consumer moves to the NBN has been a priority for the Authority throughout 2019-20 and while the rollout is nearing completion, a "better move to the NBN has been identified as a compliance priority for 2020-21".

The breaches by the four telcos relate to the Telecommunications Service Provider (NBN Service Migration) Determination 2018 and the Telecommunications (NBN Continuity of Service) Industry Standard 2018.

Under the rules, enforcement action for breaches of industry standards and determinations can include, infringement notices, formal warnings, remedial directions, enforceable undertakings, and civil penalty proceedings.