GOG won't let me reinstall a game even from the webside or GOG Galaxy.
I buyed The Witcher 3 GOTY Edition from Instant Gaming and introduced the code and played on GOG plataform.
Then I uninstalled the game and then uninstalled the aplication. The only archives that I have on the game are the ones in C:\Users\User\Documents\The Witcher 3 (the save files and user settings), so when trying to install again the game from the webside or GOG Galaxy, it says that I don't have the game on the library (like it would have on others platform with uninstalled games) or in my computer, so I can't reinstall The Witcher 3 GOTY, although I buyed the game and completed it.

there's no GOLD edition of the game, only GOTY (Game Of The Year)

thanks I've edited it

Instant Gaming is a key reseller site. GOG.com has no official key resellers.

Go to https://www.gog.com/account and check if the game is in your library.
If the game is not in your libary, it was most likely removed because the key you bought was purchased with a stolen creditcard.
Contact GOG and/or Instant Gaming and next time buy keys only from legitimate sources.

What goes for IG goes for other key resellers too. See my previous post in this thread.

Thanks, I appreciate it. Its really breathtaking that this could happened with a page like IG.
What legitimate sources do you recomend?

For GOG games there's only GOG.com, with exception of CD Projekt's own games which can also be bought at https://www.humblebundle.com/

For other games: Steam, Humble, Origin, uPlay, Epic Game Store, Bethesda, battle.net (Blizzard), Amazon, Green Man Gaming, Gamers Gate, GameStop, ...
There may be a thread about legitimate key sellers in the general forum here. A google search could also help.