The company's executive director of customer care Mark Davidson quickly addressed the error by sending out a second bulk email explaining what happened.
Attempting to explain the mishap, a Virgin spokesperson told The Press Association: "Our first email, intended for our 100Mb customers, was accidentally sent to some customers on other tiers which may have led to some confusion. We're sorry for any misunderstanding and will be writing to customers again soon to clarify how the upgrade will affect them.
"In the meantime, as part of our double speed programme we are delighted to confirm that 50Mb customers will actually be upgraded to 120Mb."
Cnet.co.uk report that apologies were also posted on the Virgin media forum last night.
The company used email marketing to break the news to customers before announcing the upgrade on any other medium. The emails explained that their equipment upgrades would be taking place from next month until the middle of next year.