Three major telcos have admitted illegally billing customers after their contracts ended.
Internet providers Slingshot, Flip and Orcon have pleaded guilty to 13 charges under the Fair Trading Act over false representations in invoices sent to consumers.
The Commerce Commission charged the trio this year, which are all subsidiaries of parent company Vocus (New Zealand) Holdings Limited, the country's third-biggest internet provider.
New Zealand's consumer watchdog accused Vocus' companies of offending during a six-year period from January 2012 to March last year.
The three guilty telcos are now due to be sentenced during October at the Auckland District Court.
The Commerce Commission's case against the companies was over invoices charging customers for a period after the agreed termination date of their contracts.
It is unclear how many customers may have been affected.
The Commerce Commission would not comment on the case prior to sentencing when approached by the Herald, while Vocus did not comment while its lawyer was out of the country.
But in an earlier statement, chief executive Mark Callander said the company had been co-operating with the Commerce Commission during its investigation.
"Unfortunately, over a six-year period, a very small percentage of customers leaving Vocus' residential ISPs who had given more than 30 days' notice of termination may have been billed incorrectly on their final bill," Callander said.
He said Vocus resolved the issue in early 2018 and has written to all customers affected, offered refunds, and apologised for the mistake.
Despite this, Callander still urged those who may have overpaid to email the Vocus refunds department if they were still owed money.
The prosecution of Slingshot, Flip and Orcon comes after almost identical Commerce Commission cases against Vodafone and Spark.
In May, Vodafone was fined $350,000 for making false representations in customer invoices.
It pleaded guilty to 14 charges under the Fair Trading Act over breaches which occurred between 2012 and 2018 and saw Vodafone customers overpay $285,000.
The Commerce Commission said Vodafone's terms and conditions claimed it would stop charging customers on an agreed date or 30 days after they gave notice to end their contracts.
Despite this, Vodafone sent invoices to more than 29,000 customers which included charges beyond the agreed date of termination.
When sentencing Vodafone, Judge Evangelos Thomas said the company's representations were highly careless.
The $350,000 fine, he added, was justified because the market needed to have faith in the conduct of its major players.
"Vodafone breached the trust that all consumers should be entitled to place in suppliers' representations," Judge Thomas said.
In April, Spark was also hit with a $675,000 fine after it admitted misrepresentations in its customer invoices and a $100 welcome credit offer.
The company, formerly known as Telecom, pleaded guilty to nine charges under the Fair Trading Act for its illegal conduct between June 2014 and December 2017.
But in its investigation, the Commerce Commission found Spark customers had overpaid a substantially higher combined sum of $6.6 million, equating to about $90 per person.
Eight of the criminal charges against Spark were for misrepresentations made in invoices, which also said bills would stop 30 days after a customer gave notice to terminate their contract.
But as with Vodafone, bills continued to be sent and were delivered to more than 70,000 customers after the 30 day termination period.
The other charge Spark faced was over promotional letters sent to prospective customers - offering a $100 credit if they joined the company and unsubscribed to a particular broadband plan.
The letter, however, gave the impression new customers could sign up online and obtain the credit but the promotion only applied to customers who phoned Spark to sign up.
Judge Russell Collins said during sentencing: "Commercial offending must be met with commercial penalties."