Gary FitzGerald, chief executive of Action on Elder Abuse, initially contacted groups telling them the deal offered by Age UK Energy "may not be all that it seems".
FitzGerald’s comments came after an article in The Times newspaper claimed Age UK’s offer, provided jointly with the company E.ON Energy Solutions, cost at least £200 more a year than the best existing energy deal for older people.
After being contacted by Age UK, FitzGerald has written to the same organisations "to set the record straight".
His latest email includes a quote by Gordon Morris, managing director of Age Concern Enterprises, which says the original email "contains inaccurate and misleading information, and that it includes unwarranted and disparaging comments about Age UK".
Morris says the original email is based on a "wholly inaccurate analysis" of the tariff by The Times, which had compared an Age UK Energy tariff with a promotional online tariff "that is not accessible to many older people".
It adds: "On a like-by-like comparison, our offline energy tariff is consistently competitive with other providers."
An Age UK spokesman said: "Because the Action on Elder Abuse email was based on incorrect information, we highlighted the need for a correction or we would need to consider more formal action.
"We are grateful to Gary FitzGerald for sending out the corrected email and are satisfied with his response."