The Australian Energy Regulator (AER) brought a lawsuit in the Federal Court against four units of Origin Energy (ASX:ORG) for allegedly continuing to receive payments from Centrepay customers, a government bill paying service, who had closed their accounts with Origin and had paid the amounts they owed, breaching the National Energy Retail Rules and the National Energy Retail Law, according to a Monday statement.

The watchdog further alleged that the firm knew that its systems were processing payments from these customers "as early as 2017," and put on hold a previously approved process that could have prevented further payments from occurring. It also failed to inform the customers about the overcharged payments or refund them within the required timeframe.

AER alleged that Origin retained over AU$2.5 million from affected customers, and the conduct resulted in over 77,000 breaches from December 2019 to March 2025.

The regulator is seeking orders for fines, declarations, customer remediation, a compliance program, as well as an independent review of such a program, and costs.

A spokesperson for Origin said in an emailed statement that the firm regretted that "it did not manage Centrepay deductions for our former customers as we should have and apologize to all those affected."

"We self-reported Centrepay overpayments directly to Services Australia in 2021, have worked closely with them to return outstanding funds to those affected, and have made extensive improvements to our processes and systems to better manage Centrepay deductions," the spokesperson added.

Its shares were up over 1% in recent trading on Monday.