The firm last month called on anyone who could prove they had suffered losses to contact them.
Managing partner Elaine Bergenthuin had said they were preparing a class action against the power utility.
Eskom said it was covered by the general public liability policy.
“No indemnity is granted by this policy against liability for: failure to supply arising out of any interruption of, variation or fluctuation in the supply of electricity which is not consequent upon damage to generation and/or transmission plant or equipment,” Eskom said.
Yesterday, De Beer said it believed it still had a solid basis for a claim.
“Given recent revelations during the Zondo Commission of Inquiry into State Capture, it seems that several key office-bearers at Eskom have been involved in corrupt activities at the parastatal in the past.
"De Beer Attorneys believe that a legal duty exists on the part of the responsible directors themselves to recoup at least some of the losses that local businesses have suffered,” De Beer said.
Meanwhile, more than 10 000 leaders in the fields of power, energy and water are expected to descend on the Cape Town International Convention Centre for the African Utility Week and Powergen Africa conference and exhibition.
High on the agenda of the exhibition, which runs from May 14 to 16, are ways to mitigate the electricity challenges currently facing South Africa.
The senior communications manager of African Utility Week and Powergen Africa, Annemarie Roodbol, said: the event was a platform to discuss issues of global importance.
“We provide a platform for the industry to discuss challenges and successes, and to share knowledge and to network.
"For example, one of our speakers believes that mini-grids are the answer to South Africa's load-shedding problems.
"The programme for 2019 follows the industry trend of connecting the full value chain and reflects the many disciplines required for a modern, smart power industry,” Roodbol added.