C3 won't surrender (Golden Rainbow)

Hello to all,
i'm trying to conquer a C3, it's war index i about 7. I read that a C3 will fall under 25. Is correct?

Only for the first one that you capture (like a kind of starter's bonus). After the first one, you need to beat the others down to zero.

Ah! I understand now. Thanks a lot Danneh

It is wierd, my first C3 didn't surrender until I beat the war index down to 0.

And my costs of taking it over is not as low as I read.

Yeah but look at that construction you need now.