Can you imagine being told that you can’t access your emails for the next three weeks? No access to work or family messages, your expensive holiday booking, or the tickets to a gig that were emailed over. What would you do?

That is the situation a number of Virgin Media customers say they have found themselves in this summer, and it has left some so furious that they are threatening to not renew their broadband contracts.

For others, this has been the wake-up call to ditch their old email and finally move to Gmail, Outlook (Hotmail) or another standalone service. So much of modern life now revolves around email that it is a nightmare if it stops working.

Problems started on 19 June when Virgin Media upgraded its systems, and affected people using the old NTL, Blueyonder and Virgin email addresses.

A tech failure initially left some people unable to send or receive emails for several days, and then meant some had three to four weeks without access to historic emails – causing panic among those planning to go on holiday or attend events that relied on emailed tickets.

Virgin Media, which apologised at the time, told Guardian Money this week that all the problems relating to the “outage” were resolved by 17 July. Despite that, Money is receiving complaints from customers who say they cannot access their emails.

Harriet Lane from London lost her email service in June. Although the ability to send and receive emails was restored a few days later, she says she had to wait more than three weeks for her historic emails to be restored.

“At one point I thought they were all lost – vital plane and entertainment tickets that I needed imminently, plus 20 years’ worth of work contracts and important legal documents. I was so relieved when it came back but it was a nightmare. I have repeatedly put off switching email address, fearing I would lose all my emails, but this may be the spur I need. I shouldn’t have to do it but I can’t go through that again,” she says.

Daniel Somogyi from Dorset, who pays Virgin Media £100 a month for his home package, says he suffered the same fate and that the whole episode caused him “a great deal of anxiety and inconvenience”. At one stage he feared being unable to take flights to Canada as the tickets had been emailed to him, although the service resumed just in time.

David Winskill from Crouch End, north London, says his problems are ongoing. His Blueyonder email address, which he has had since the early days of the internet, stopped working on 18 June. Days later the service was restored and 450 emails landed in his inbox. However, he says historic emails, such as letters to GPs and local council work that were kept in folders, have still not returned.

“I’ve been around the world talking to Virgin staff but no one seems able to fix it. Every week I have escalated this up the management chain, to no avail,” the 68-year-old says.

The Virgin Media customer Anna Gutkowska told us she had had to travel to Nottingham to go to the office of See Tickets in a desperate attempt to retrieve a ticket to a festival happening that weekend. She said she was unable to access her two NTL email accounts after they stopped working.

“I rely on email for everything – professional subscriptions, banking and for purchasing. I am supposed to be going to a festival at the weekend but couldn’t access the tickets. This is causing me so much stress,” she wrote last weekend.

Tilly Evershed from Oxfordshire contacted Guardian Money after spending several weeks unable to access her NTL email account. After we raised her case this week with Virgin, the service was restored, but only if she uses a password given to her by the company. She says she remains unable to change it to something of her choosing, thereby leaving her emails unsecure.

Like the others we spoke to, she says the biggest part of the problem is that it is difficult to find anyone at the company who is able to help.

A Virgin Media spokesperson says each case raised by Guardian Money has been or is being resolved.

“Following an outage, we quickly restored email accounts so users could continue to send and receive emails as normal; however, a small proportion of individuals were unable to access historic emails. We have been in regular contact with these account holders throughout this issue to apologise and keep them updated on our work to fully restore their inbox, and this was completed last month. We apologise again for the inconvenience caused, for the time it took to fully resolve this, and to any customer who did not receive the help they needed.”

This is not the first time Virgin customers have been unable to access their emails. There is a good explanation on how to switch email addresses without losing emails at the website.