Telco giant Vodafone has been fined $165,000 for misleading pricing over its Red Essentials mobile phone plan.
The Commerce Commission filed charges against Vodafone in May this year after it was discovered 15,000 customers were overcharged a total of $92,000.
Most of the customers were overcharged less than $1 each. All have since been refunded.
"Overcharging a large number of customers a small amount can result in firms receiving large sums of money they are not entitled to, so they need to be vigilant to avoid misleading consumers and breaching the Act," says commissioner Anna Rawlings.
The charges related to the Red Essentials plan in August 2013, when subscribers were told their monthly cost would be reduced by from $79 to $69.
However, Vodafone's billing system did not apply the $10 discount.
This is Vodafone's fourth sentencing under the Fair Trading Act in the past five years.
The biggest fine, $960,000, was in relation to advertising campaigns that ran from 2006 to 2009 for various broadband and mobile phone promotions.