Virgin Media has been told to issue refunds to over 100,000 people.
ComReg has handed down the penalty following an investigation into so-called Post-Cancellation Charges.
The regulator found that Virgin was still charging the affected customers even after they had cancelled their contract.
ComReg says "The company failed to proactively refund customers and instead retained the monies in inactive accounts."
The average refund per customers is €33, and ComReg says this should be paid back by the end of March.
Virgin Media has responded and says it does take regulatory compliance extremely seriously.
It is Virgin's position that it is in full compliance with all our regulatory obligations.
