hello i buy s2 from website then i enter the cod on Redeem an LFS gift voucher
on old demo user then show message typying the cod is correct then nothing happend so what shuld i do i buy this one becus my old s2 is somone stolen it now i dont knwo what i do please help me

if you are writing it from the account, where you entered coupon, then that account now says "S2 licensed", here in forums. So it went well.

Now you need to unlock the game installation on your computer with this account, using the GAME password (the LFS account here on web allows you to use two different passwords, one is WEB password for lfs.net and forum, second is GAME password for lfs.exe, so you can have two different to prevent easy steal of account (make sure the WEB password is stronger and keep it secret).

Here is the FAQ about unlocking the game: https://www.lfs.net/faq/3