GalahadLePlateux: Ok, support answered that they can't refund (obviously) but they offered me a gog wallet refund, which i won't take since i will definetly play the game now that i downloaded it. Not having it in my steam library will be a little unconvenient, but i'll get over it :D. The thing is that i think i already have too many launchers (steam, battle net, epic games, wargaming, uplay,...) it's starting to get messy, that's why i try to have as much games as i can in the same place, which is the easiest : my steam library.

Anyway, thank you all for your answers !

BlackThorny: I up-voted you for the honesty alone, you seem to be a good person and nice to welcome you to Gog!
I do wonder however, what game you are talking about :)
{Seems you already familiarized about your Gog Profile - as you made your 1 Games list private}