It seems that the Launcher/Hook is not the issue here, I can connect to the backend servers via my regular internet con.
I tried reinstalling the Launcher and every hooking option i could find, no success.
I suspect this free VPN service does only support a limited variety of application connections, Steam would not let me login while Spotify, Thunderbird and Firefox worked fine.
You don't happen to have suggestions for other free services?
Thanks a lot for your reply! I tried a free VPN service (Shellfire) and I am now successfully posting this message from a proxy server in the US (instead of Germany).
Tried to log into C&C, "Could not connect to backend server."
What is weird: My actual (new) IP seems to be "162. [...]", but in game I could only switch to something "10. [...]".