Sky Television has apologised after being warned by the Commerce Commission for over-charging some customers who were promised a cheap deal.
The commission says subscribers were offered an upgrade to a premium channel for one month for $1, with proceeds going to the Starship Foundation.
But 2633 customers who used an interactive voice recognition phone service to sign up were charged $25. They were later refunded.
The commission's competition manager, Greg Allan, says the company possibly breached the Fair Trading Act but because Sky TV co-operated and immediately returned or credited the money, a warning was the best option.
Sky Television says it is sorry the overcharging occurred and steps have been taken to ensure it will not happen again.
Head of corporate communications Kirsty Way says the company is taking the matter seriously.
"We act quickly on these things and make sure that we keep our customers happy. We like to attract subscribers and provide a good service to them. The last thing we want to do is in any way to have them unhappy".