PookaMustard: It doesn't matter if the copy they 'pirate' are not theirs. What they're 'pirating' is the same bunch of zeroes and ones that forms the original copy, sometimes with a crack depending on the DRM in question. And if that is still a problem, perhaps because the support team might ask about the authenticity of the game copy, you can still convert the 'pirated' copy into a regular copy by letting GOG Galaxy know that this version of Witcher 3 is downloaded and then ordering it to repair or verify the game data, thus converting it to 'their own copy', as I said before. Since they own the game, that shouldn't pose anything on them.
darthspudius: But it is still an illegal copy whether your want to try get round it or not. You're still taking someone else's copy from a website that is very likely banned in so many countries for a reason. But saying that, this kind of thing shouldn't have to happen because GOG is perfect.
And where did that someone else get their copy from? Sometimes it might be the same download the OP is unable to finish, from GOG. By that logic, I can't give a friend the installer of Witcher 2 from GOG in an already downloaded form, even if we both own the Witcher 2 on GOG, because its my copy and not his, even though there are no strings in the installer saying this installer belongs to PookaMustard and none else or whatever.
I'm not playing with DRM'd installers here. And I'm not sure how torrent websites are banned in so many countries. They're supposed to be everywhere. Again, 'this someone else's copy' can be converted to 'yours' easily. What matters is that the OP already owns the game on GOG. I'm not saying that they should torrent all their owned games from now on, but I'm saying I don't see what is wrong in that versus outright pirating the game without owning it legally.