Calling them is definitely the way forward - the delay could just be because they're trying to look into the technical issue and work out how to address it as the issue was unexpected.I’d honestly reach out to them via Linkedin if they’re not responding via email. I messaged Shaun on Linkedin last year for an urgent matter and he was very responsive. Otherwise you could always call reception and they can connect you to the early careers team as a last resort. Hope it gets sorted for you soon!