Three major telecom giants have pleaded guilty in court following an investigation by regulator Comreg.

Eircom and Vodafone have been convicted and fined for continuously sending customers over-charged bills.

The telecom giants, along with Three Ireland, pleaded guilty to charges under Section 45 of the Communications Act.

Barbara Delaney is the director of retail of consumer affairs at ComReg.

"It is a good result to the extent that, from the point of view of the consumer, if there is an issue with their bill and they complain to an operator we're confident - on foot of yesterday's events - they should not get a resolution speedily", she told Newstalk Breakfast.

In all cases, it was to do with either charging too much for a service, charging for a service that the customer did not want or order, or charging for a service that was no delivered.

"Once Comreg got involved, the customers were refunded...however, there was no resolution before Comreg got involved so the customer themselves could not achieve this".

She told Breakfast there were also cases involving debt collectors over amounts customers were contesting.