There are an estimated 76,000 customers who may be due refunds
Eircom has been hit with a 2.45 million euro penalty for overcharging customers.
The company, now known as Eir, will refund customers and also make changes to its billing practices.
The Commission for Communications Regulation took enforcement action against Eircom and says the company has committed to paying a 2.45 million euro penalty.
Eir's also implementing a series of 'backward looking measures' , where it will identify customers who were incorrectly overcharged historically and have not been refunded.
There are an estimated 76,000 customers who may be due refunds, valued at 6.7 million euro.
The focus will be on customers incorrectly charged due to a broken bundle on the customer's account and where customers were charged after requesting the end to their service.
It'll also look at those who faced early cease charges when they were allowed to cancel without payment.
The company will appoint and Independent Auditor to review the effectiveness and implementation of the measures.

Council Acquired Seven Derelict Properties Through Compulsory Purchase Orders Last Year
Investigations Continue Into Beauty Brands Sephora And Benefit Over Marketing Issues
Parents Association Call For Urgent Action Over "Unsafe" Maynooth School Car Park
Minister Martin Heydon Calls On EU To Be Flexible On Levies For Fertiliser
Gardai Have Arrested 3 People In Relation To Man Last Seen Alive In Monasterervin In 2019
80% of Public Sector Workers Cutting Back On Essentials, Survey Finds
Naas Clinic Among Highest Earners From Medical Cert Scheme
Kildare-Based Animal Rescue Group Continue Calls To Ban Sulky Racing On Public Roads