Mobile phone operator Three has to refund a total of €824,765 to 26,000 customers who were charged for a premium rate service that was not supplied to them.
The move follows a negative finding by the communications regulator, Comreg.
It found that Three had not complied with a number of its obligations under the Premium Rate Services (PRS) code of practice and PRS licences.
Thes include that the provider of PRS must make all reasonable endeavours to ensure that services provided by them are of a sufficient technical quality "so as not to
cause end user harm and to ensure compliance with the requirements of the code."
It also requires providers to ensure end-users are not charged in respect of PRS that were not supplied.
This includes, for example, circumstances where service provider deliver a "busy tone" or "silence" prior to connection to the requested PRS, Comreg said.
Users must also not be charged for the receipt of error messages, according to the code.
However, following a probe Comreg found Three had not met the requirements in relation to a particular premium service and ordered it to refund a total of €824,765 to 26,000 customers.
Three has until April 16 to complete the refunds, equivalent to almost €32 per customer concerned.