A major energy provider will reimburse more than 24,000 Southeast Queensland customers for late fees it incorrectly charged over a five-year period.

AGL reported to the Queensland Competition Authority (QCA) that it had charged $12.73 late payment fees to many of its customers, often on more than one occasion, between 2015 and 2020.

The late-fee charges contravened Section 22A (4) of the National Energy Retail Law Act 2014, which prohibits the imposition of late payment fees for Queensland electricity customers on a Standard Retail Contract.

After identification of the contravention by QCA, an internal investigation by AGL revealed that the energy provider had unintentionally charged late payment fees to 21,144 residential customers and 3,286 small business customers on a standing offer, the company stated to QCA.

The total value of these fees tallied more than $780,000 and has begun to be refunded to existing and former customers who were impacted.

AGL has advised they will automatically credit the amount on the next bill of impacted customers.

For impacted customers who are entitled to excessive refund amount, AGL said it will directly refund to their bank account.

AGL will attempt to contact impacted customers who are no longer with the provider.

QCA Chair Professor Flavio Menezes said it is important that electricity retailers meet their obligations regarding customer protections.

"The QCA encourages any former AGL standing offer customers who have been charged late payment fees to contact AGL to find out whether they are entitled to a refund," he said.

If you are a current or former AGL customer and have been contacted by AGL or believe you may have been affected, please go to agl.com.au/qldlpf for more information. Alternatively, contact AGL directly on 131 245.

Originally published as 24,000 to get refund after Qld electricity bill stuff-up