I believe each sim deal has its own account, so probably a good idea to send a PM to one of the Plusnet staff regularly replying on the Mobile help board advising them of your son's account details (otherwise they won't know where to start looking.)
Is it an iPhone or android? I've had data issues with my daughters iPhone and Plusnet said they couldn't help, despite the issues only starting when I went to Plusnet. I resolved the problem but it needed a full factory restore and then I had to restore each individual app backup. I'm convinced the issues are to do with the APN settings, which you can't access/view on an iPhone, but Plusnet's solution is to send another non-working SIM!
