Network operator Creos and its parent company Encevo said they were still "analysing the damage" following a cyber attack on the night of 22 July.
During the attack, the hackers extracted a large amount of data from the supplier's computer systems, as well as rendering parts of it inaccessible.
Encevo said the group was currently making every effort to assess the damage and analyse the hacked data, but that it did not yet possess all the necessary information to personally inform those affected by the breach.
The energy supplier went on to ask customers to refrain from contacting the group on the topic for the time being. A website has been set up to provide assistance, with updates as the situation evolves.
Creos and Enovos apologised for the inconvenience and added that the electricity and gas supply would not be affected by the issues.