All info on student discounts including TOTUM, is in this guide.
You have 28 days from purchase to apply the discount.
If you are having any issues at all you need to call O2.
Numbers here Guide: Coronavirus Community Help and Support
Advice from an O2 Guru regarding a way to get through:
If you call 202, when it comes to the reason you are calling stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to an advisor.
Press Upgrade, Lost/Stolen or Fraud if you have to.
*The Game Is On*
Track usage, upgrade and get support with the My O2 appDownload My O2