This campaign was in December and it lasted for one day. Hence the redemption of the code after the campaign ended is not possible.
I have the same problem:
I got the code from chip.de on the 24. of dezember and I installed and activated the software the same day (24.12.2018) I then got the message the subscription is valid until 29.12.2019.
A few days later when I wanted to use the software I got the message "subscription expired".
When I want to reactivate the code i get the message "code not correct"
I uninstalled the software and I installed it again, then the subscription recogised the previous installation and the serial number and it was again valid until 29.12.2019
two days later the same expired subscription .... installing again ...... valid again.
It always lasts one day befor the subscription expires.
And I also see the network adapter for freedom vpn as unidentified network when.
Please help me.