Auckland lines company Vector is dismissing a call it should refund customers nearly 14-million dollars immediately, instead of over the next two years.
The Commerce Commission found Vector guilty of overcharging nearly 30 percent of households between 2014 and 2015 by not switching them to the best rate.
Vector agreed to earn less revenue and keep affected residential power prices the same for the next two years to pay back its customers.
Power retailer Mercury said households deserved to get their money back now.
Responding today, Vector said the repayment plan it decided with the Commerce Commerce was the most reliable way to ensure customers get their refunds, because there's no regulatory power to force retailers such as Mercury to pass those refunds on.
It said it could not unilaterally switch consumers to the best rate, and it relies on retailers to identify them and request a switch.
Vector said that in many cases, retailers did not do that.