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".
Revision App offers animated videos and quizzes to help with exam revision. The Revision App website includes the logos of four major exam boards, but they have all told the BBC that they have nothing to do with the service and their logos have been used without their permission.
Another discrepancy is a promised discount on access to GCSE videos. The website calls it a "1 day sale" yet it has appeared on consecutive days over 24 hours apart.
