Vodafone has been fined $165,000 after pleading guilty to making false price representations.

It’s the fourth time the company has been fined under the Fair Trading Act since 2011.

The latest charges were brought by the Commerce Commission over bills Vodafone sent to customers who signed on to its “Red Essentials” mobile plan between January and December 2014.

Vodafone launched the $79 Red Essentials plan in August 2013. It later dropped the price to $69 the following January. But about 15,000 customers missed out on the $10 discount.

The commission says affected customers were collectively overcharged approximately $92,000, although the majority were overcharged by less than $1 each. Customers have since been refunded.

“It is vital that businesses invest in making sure they have strong compliance processes that can support these types of promotional offers, particularly when selling products to a significant customer base,” commissioner Anna Rawlings said.

“Consumers rely on companies to invoice and debit them accurately, as many do not check the finer details. 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.”