Eep! Thats a big mistake I made when I first got my Bella. The trick is to comb BEFORE the fur gets wet, or else it will make it 10x harder to comb out. Try using a slicker comb. But make sure you get it all out before making him wet. It isn't like our hair where if we put conditioner, you can feel your hair loosening up, its different and really the opposite!
My first mistake I had to get Bella shaved down due to all the Matts, so hopefully me telling you this will avoid that.