Eircom has apologised to customers who were falsely told in a letter to their homes that they could save money by switching to flat-rate internet service.

In a personalised letter, sent to 35,000 Eircom customers with their latest bill, the company said "we have recently reviewed your internet charges", and "based on your usage" the relevant customer would save "up to 47 per cent on the charges you are currently paying". But Eircom admitted yesterday that the letter was only sent to customers spending an average of €3 to €10 a month on internet usage - none of whom would have qualified for a saving by switching to the flat rate.

An Eircom spokeswoman said: "Unfortunately, there were a number of customers to whom the letter was sent who, by virtue of their low usage, would not have applied for the saving without increasing their usage.

"We do accept the letter could have been clarified, and that the offer could have better explained to customers. But there was no intention to mislead."

A further 25,000 Eircom customers received a similar letter promising a saving of up to 47 per cent on the flat-rate service "based on our analysis of your internet activity".

One such letter told the recipient he was spending an average of €13.38 per month on Eircom's pay-as-you-go option when his phone bill told him he was spending less than half this amount. The Eircom spokeswoman said the case was being investigated.

She admitted that there were errors with the second batch of letters, and said the company had apologised to customers on similar grounds.

The Advertising Standards Authority for Ireland said yesterday it had a received a complaint on the matter and was considering it.