An error at state-owned electricity company ESB meant that Meta was massively undercharged for electricity at its Clonee data center in Ireland.
The ESB blamed the mistake on a substation technical fault, which meant that only seven percent of the data center's energy use was recorded over an 18-month period.
The facility uses the same amount of power as 150,000 average homes.
The energy regulator admitted the problem at the Oireachtas Environment and Climate Committee this week, but said that it was still checking if it had uncharged others.
Karen Trant, director of customer protection at the Commission for the Regulation of Utilities (CRU), told the Irish Independent that ESB Networks (ESBN) were also still trying to work out exactly how much Meta had been uncharged.
“Our concern is that we would want to know that it’s not systemic, that it’s isolated to that particular site," she said.
"What ESBN are saying is that they are confident that is not a systemic issue, however, they can not guarantee that it has not happened on another site."
Once the undercharging has been fully calculated, Meta will be told to pay for the free electricity.
Last year, Ireland's state electricity grid authority EirGrid called a halt to plans for up to 30 potential data centers due to issues meeting the electricity demands of the growing sector.