In recent weeks, thousands of Irish mobile phone users have been hit with the calls, which is a common form of fraud worldwide.
While many mobile operators block the numbers once identified, customers have also been warned that they are responsible for all calls they make and will be billed accordingly.
The scam involves a fraudster calling numbers — often using an autodialling machine — from another country. The call will hang up after one ring in the hope the person who gets the missed call will ring back. If the person does so, the objective is to keep them on the line as long as possible in order to generate revenue for the fraudster. The victim of the scam will suffer the consequences on their next bill.
Three is advising customers not to answer or return calls to numbers they do not recognise. However, it also warned customers that they are ultimately responsible for the calls they make.
“If a customer has been affected by this we would encourage them to contact us to report it. Customers are responsible for their own usage,” said a statement.
Eir said the scam is an “industry-wide problem” and advised customers not to answer or return calls to unknown foreign numbers.
“There is no charge incurred when people answer calls from these numbers, only when they call back, and the longer someone stays on the phone the higher the charge will be,” it said. “Eir proactively prevents customers from calling known fraudulent international numbers and we block new numbers as and when they become known.”
Vodafone has issued the same advice and is blocking fraudulent numbers.
ComReg said victims who are worried about the impact their error will have on their bill should contact their phone operator: “If a customer has a concern in relation to their bill they should contact their provider. The mobile network providers are also aware of the scam.”