Esat Digifone has overcharged thousands of customers because of a mistake with its pricing system for 1850 numbers.

Since October Digifone has charged 24 pence per minute for calls made to callsave rate numbers instead of the correct 24 pence flat rate.

Callsave rate numbers have grown in popularity in recent years and are used for customer care and certain other services.

An Esat spokeswoman confirmed last night the company had discovered its mistake and would rectify the problem within the next few days.

She said several thousand people may have used such numbers but many of these could have been undercharged as well as overcharged.

"Customers who have called our customer care helpline will all receive refunds," she added.

Meanwhile, telecoms regulator Ms Etain Doyle intervened in a separate telecoms pricing row involving cable company Chorus yesterday.

Ms Doyle has asked cable company Chorus for an assurance that it will not introduce costly maintenance charges.

It emerged yesterday that Chorus is proposing to introduce an additional monthly £2.50 maintenance charge for its customers from March.

Customers who do not pay this charge would face hefty fees of up to £45 if they use the Chorus call-out service to fix or maintain their television services.

Under the terms of Chorus's cable licence the company is not allowed to introduce any price rises without receiving consent from Ms Doyle.

But Mr Willie Fagan, managing director of Chorus, and a former director of consumer affairs, said yesterday the charges were justified as they were not price increases.

"Under the current regulatory structure we can't change prices for the service," he said. "But this is a charge for maintenance."

Mr Fagan said the charges were necessary due to the high costs involved in sending out engineers to rectify faults.

However, it is understood the telecoms regulator considers the charges to be a price increase by the back door.

A spokeswoman for Ms Doyle said last night the charges had not been approved in accordance with the terms of Chorus's licence.

"The director is looking for an assurance that the charge will not be implemented," she added.

Since Chorus began informing customers of the new charges this week, more than 30 complaints have been received by the regulator. The huge costs involved in rolling out digital TV services by both Chorus and NTL are understood to be putting the two firms under pressure.

Only last month NTL announced it was delaying its rollout of digital services in the Republic.

Industry sources last night suggested the additional charges proposed by Chorus were a product of the cash squeeze affecting the sector.