Commerce Commission chair Anna Rawlings said in many cases customers would not be in a position to easily identify whether an error had been made when they were invoiced for goods and services and customers should be entitled to assume they were being charged correctly.
"Businesses must make sure that they have systems in place to ensure that customers are charged accurately, and to identify and correct inaccuracies promptly if they arise."
Genesis had reassured the Commerce Commission it now had an audit system in place to minimise the risks of a billing error occurring again.
Last week ASB confirmed it would repay $8.1m to customers after admitting lending failures following an investigation by the Commerce Commission which found it in breach of the Credit Contracts and Consumer Finance Act (CCCF Act).
The bank could not give assurance that proper disclosure was given to more than 73,000 home and personal loan customers when they made changes to the relevant repayment date, amount and frequency of their existing loan agreements either in a branch or over the phone.
Genesis has been approached for comment.