Youngsters from Whitley's Christ the King School paid to see Diversity top the bill at the Love Can concert at Reading University's Students' Union last week and were even given VIP front row upgrades to get a closer look and an invitation to meet the stars backstage.
But halfway through the concert it was announced that Diversity would not be performing, and this week promoter Raphael Obrike admitted he knew two days beforehand that the Britain's Got Talent winners were not coming.
The concert, a fund-raiser for Macmillan Cancer Support and The Royal Berks Charity, was also supporting fellow Christ the King pupil Yanne Nkurunziza, who has cerebral palsy and needs £50,000 for a life-changing operation.
Jo Cyrus, from Whitley Wood Lane, took son Malachi, 10, and his three friends. She said: "I think it's disgusting. I bought five tickets at £10 each and we were so looking forward to it.
"My son broke his toe the day before while playing football at school, so he was in a wheelchair and we were called over to the desk when we got there and asked if we'd like a free upgrade.
"We were taken to the VIP area and given front row seats, and we sat through all the performances when someone suddenly came on stage to say that Diversity weren't able to make it."
She added: "We thought they were just mucking about at first, but the children were in hysterics, they were so upset. People are absolutely fuming because they paid to see Diversity."
Love Can promoter Mr Obrike said: "Diversity are involved in a contract with a television company and we were warning people when we gave out flyers for the show that they may not be able to make it if it clashed with their schedule.
"I sent an email to all of the people that bought tickets online as soon as I knew they couldn't make it and offered refunds, but I did not have contact details for everyone. Unfortunately, it had to be announced on stage."
Mr Obrike said he is trying to make refunds to fans who expected to see Diversity and added: "I am a community person and I do not want anything to dampen my reputation."