3 month old feeding

(from the UK) My baby is 14 weeks old and is bottle fed. We had him on the cow and gate hungrier baby milk and he would drink 8oz every feed but recently it has been out of stock EVERYWHERE. We were then told from someone that they had stopped making this milk so we rang our health visitor and she said just to change brand so we switched him to the aptamil hungry baby milk but now he doesn't have the full 8oz. He will only have about 3/4oz each feed. Could this be because he doesn't like the milk or could the milk just be having a different effect on him?