Prongs should not be used unless a very last effort. They have much more negatives then positive.
Try using a head collar -halti, control ease, gentle leader. This head collar goes over the snout and still allows the dog to eat, pant, basically keep its mouth open. When the dog pulls he will automatically pull it's head sideways and find it uncomfortable.
I have a dog who is the most stubborn dog on pulling and this is the only thing that works. Head collars aren't meant to be used as a crutch, it's a training tool, eventually you should go back to using a flat buckle collar.