School children have been left very upset after their JLS tickets weren't valid because they were from an illegal website.
Charlotte and Nadine both really love JLS, so when their mum heard they were playing in their hometown, she decided to buy tickets.
But the website she bought them from was fake and had nothing to do with the band - or the concert organisers.
Loads more fans have been taken in by an illegal ticket site scams.
Advice for buying tickets
Indira Pereira-Lopes works for the Office of Fair Trading - a group who who try to stop scams like this one.
She reckons you should ask yourself if the deal you see on a website is too good to be true, or if the tickets it is offering are sold out on all the major websites.