Halti No Pull Harness - Stop Your Dog Pulling on The Leash. Adjustable, Lightweight and Easy to Use. Reflective Dog Training Harness for Medium Dogs (Size M, Cobalt Blue)

I can't help you with the behavior; it's very concerning and I've unfortunately got nothing for you there. BUT! I think you really need a body harness. It both keeps the pressure completely off their neck and also gives you a WAY better control level. Here is one example, though it sounds like you need an even stronger version. I wish you all good luck. https://a.co/d/02WUVRv8