Labour bosses will not extend the party's leadership election vote deadline of 12pm on 10 September despite complaints from some members and supporters that they have not received their ballots.

A Labour spokesman urged people to check their email spam folders and insisted to IBTimes UK that the party has sent ballot papers to all eligible voters and reissued them to members and supporters who contacted the party.

"[We have found] quite a lot of people aren't actually eligible for a vote in the first place, who were speaking out on social media," he said. "People who are genuinely missing their ballot can contact the party via email and we will try and sort out what we can. We are confident that the ballots have gone out to absolutely everyone now."

But Will Coldwell told IBTimes UK that, despite Labour reminding him via email to vote in the contest, he has not received his ballot. "I previously contacted the party to let them know I hadn't received my ballot by post and was told I would receive it by email. I've had emails reminding me to vote (so I assume I'm on the system and haven't been purged) but no ballot has arrived," he said.

The London-based journalist described the situation as "very annoying" and said it was a "shame" the process has been "so badly managed" by the party. "I hope that those who haven't received ballots still are in a minority – and that there is a clear winner – because it will be frustrating to think it could have an impact on the results," Coldwell added.

Labour leadership election explained in 60 seconds IBTimes UK

Mark Hemingway, who joined the party in early August, told IBTimes UK: "I'm a card-carrying member so I should be entitled to vote." The Oxfam volunteer also revealed he planned to give his first preference to Yvette Cooper in the leadership contest and Stella Creasy in the deputy leadership race. "I have no intention of ever voting for Jeremy Corbyn," he added.

Hemingway claimed he had emailed Labour twice to alert them of his issues but he had not received a reply at the time of publication.

But Cooper's camp told IBTimes UK the issue is not a "massive problem" for the leadership hopeful. A spokeswoman said: "We haven't got evidence to suggest that there is a huge number of people [who haven't received their ballot], and we hope the party are still responding to people who get in contact."

However, Andy Burnham's campaign chief described Labour's decision to close its helpline for the election as "unbelievable". Michael Dugher, Labour's shadow transport secretary, said: "With thousands still to vote [and] many not had their ballot, Labour has closed the call centre to help members trying to vote. Unbelievable."

The result of the vote will be announced at a special Labour leadership conference on 12 September. Front runner Jeremy Corbyn is expected to succeed Ed Miliband on the back of a left-wing surge in support.