Importing creates a new set of products every time

I've set the first Column to KEY (GTIN)
The first column in my csv-file is the GTIN

Every time i parse the file new products is created. I want them to be created the first time and then updated, what could be wrong?

Yes, it's correct logic.
The plugin will try to find existing product using this key (Gtin).
Change the parameter Action  with the value  'Insert and Update'.