Students using an exam revision app say they have been charged repeatedly, even when they no longer need it or have not been able to use it.
Revision App claims to offer effective online revision through its website or phone app.
A BBC investigation has found the company has taken people's money then failed to respond to their complaints.
Its founder said the cases were a "poor representation of the experience customers actually encounter".
Entrepreneur of the year
Revision App offers animated videos and quizzes to help with exam revision. It was set up in 2011 by Jermaine Hagan.
