The big red “DOWNLOAD FILE” button is an AD — it won't give you the game. The real links are the purple “Download Here” buttons under each mirror (DATANODES, GOFILE, etc).

1. Pick a mirror and click its purple “Download Here” — not the red “Download File”.
2. First click opens an ad tab — that's normal. Just close that ad tab and click “Download Here” again — the second click takes you to the real file.
3. Ignore any other pop-up that opens — close it and go back.
4. Confirm the downloaded size matches the GB shown. A few MB = fake, delete it.