Holder kicks the ball

On a field goal try, the ball is muffed by the snapper and it lands on the ground. While the ball is on the ground, the place kick holder kicks the ball and it goes through the uprights. Is this legal or is it illegal kicking? If illegal and the opponents decline the penalty do you score the field goal?

Illegal kicking and you cannot score except with a legal kick. They may decline, but no score.