Spark has pleaded guilty to charges relating to historical operations and billing issues.
The first issue was an incorrect application of 'welcome credit' when some customers joined Spark in 2016.
The other was an issue with billing, relating to a 30-day notice period when customers left the company.
There was also a third charge regarding data billing for some customers in 2015, but it was dropped by the Commerce Commission.
The Commerce Commission laid 11 charges in June against the company, alleging it made "false or misleading representations relating to its billing and a $100 offer for new customers."
In some cases, customers were given the required 30-day notice to terminate their contract, but were charged for the entire next month regardless of when their Spark service stopped.
Spark has released a statement saying the issues were all mistakes, and there was never any aim to trick or misinform customers.
"These were all system-based errors caused by genuine mistakes with no malicious intent involved on the part of Spark."
It said it had done its best to reimburse customers who had been caught up in the errors, but "some of these customers left Spark a considerable time ago" and their contact details had changed.
Spark managing director Simon Moutter said in July that the company was "deeply disappointed that the issues affected our customers."
"Given the unintentional nature of the errors involved and the extensive actions already taken by us to put things right for our customers, we are obviously disappointed the Commerce Commission is now embarking on what will be a costly, time-consuming court process," he added.
Spark said today that it didn't expect any penalties to affect their financial position for the 2019 financial year.