Hey ho, i bought witcher 3 last year and i allready played it...
but today i want to download it and it wasnt in my libary anymore:(:(
pls help me...i dont know what to do...

Where did you buy the game? If not GOG, you need to contact the store you bought it from, as the code may have been stolen. If you bought it from GOG, contact support.

Yes I bought a Key...but I allready has activated it...so the Key is used and nobody is able to steal it isnt it?!

It's not about a stolen Key but stolen credit card data... the transaction in which the Key has been bought by the reseller might have been bunked due to that, and it may be the reason for the low selling price of such keys. You've been had.

We've seen tons of such problems in the Witcher 3 subforum alone by the way. You are definitely not the only one who got screwed over.