Minecraft code has already been redeemed?

Yesterday I bought Minecraft voucher for Windows 10 at Saturn. When I wanted to enter the code I noticed that my code only had 10 characters and when I entered it it appeared that it was already in use. (later I tried it on https://account.mojang.com/....com/login too, but when I first wanted an account it was automatically transferred to the Minecraft website and a Mojang account can't be created there either.

I also checked the Minecraft "Support" but there was nothing helpful.

I don't know now whether to contact my Saturn, Mojang or Microsoft.

You have to turn to Saturn. Usually A voucher is automatically activated immediately after the payment process. But then something went wrong.