I thought I was going nuts, but I am not the only one.
Long story short: I am a registered user, but I ordered a server as a new customer because when I tried to log in, it redirected to the CCP panel. I thought this was normal behavior, so I just went back to the order page and saved my address again, but Netcup canceled my order (where I also used my voucher code, by the way) because I ordered it as a new customer and I should have done it as a logged-in user instead.
So now my voucher code is useless, I can’t redeem it again and I can’t even order a server because of this issue. I’ve tried different browsers, but the outcome is the same.
Could anyone shed some light on this?