Telecom internet customers are furious after being left without email over the weekend during a major upgrade of the service.
The company says it is enhancing the overall service to more than 500,000 Xtra customers and had tried to notify people of a 24-hour webmail outage.
But some customers said they knew nothing of the work and, when they rang to complain about loss of the email service, were unable to get through to the helpdesk.
There have also been other technical problems, which Telecom says could be expected with such a massive "technological migration" to the new Yahoo!Xtra Bubble service.
The result of a partnership between Yahoo! and Telecom, Bubble is touted as providing "an exciting range of new services that will change the way you use the internet" for no extra cost.
But Xtra customer Stuart Campbell, of Cromwell, said he had heard nothing of the outage or Bubble and it had caused him plenty of headaches.
Unable to access his email via webmail on Saturday, he turned to Mailwasher, a spam-filtering service, only to find his usual email files reduced to 19 spam emails and an email informing him of the new Bubble service.
He tried webmail again yesterday and was asked to go through a "whole rigmarole" of registering for Bubble.
"This change appears to be a unmitigated disaster ... [It] appears to be getting forced on us - it's not optional to take it or leave it."
Mr Campbell said he spent almost two hours contacting the Xtra helpdesk only to be told by an operator that he should try again today. He was told hundreds had been calling with similar issues.
A Telecom spokesperson said the upgrade to Bubble was timed to cause as little inconvenience to customers as possible. Weekends are traditionally lower email usage times.
The company was investigating the unforeseen "teething issues ... as a matter of priority".
Herald technology writer Peter Griffin said Bubble was announced the same week as rivals such as Vodafone upped the ante in the broadband industry.
Telecom needed to differentiate and keep customers loyal. If there were genuine problems with Bubble it could "come back to bite them".