If the code doesn't work regardless of what you do then it's been stopped by zavvi, which should be the same for every customer.
If code works for some and not others then it's to do with your own settings on your phone/PC/Laptop/iPad etc, which you need to change or mess with at the time.
The other day I was questioning the code not working and Paul came along and made a suggestion regarding clearing the cache / refreshing on whatever device it is you use.
I have tried this today and it worked for me using a PC.
Granted, not everybody has access to PC at a particular time, but for next time (or for Thor 2) in advance find out how to do this for each device you may use.
Sometimes it might just be unlucky that you can't use it.