What can I do legally to get my son away from him ASAP?

My ex has sole custody, has been with holding visitation for 6 months now and he won’t communicate with me at all about anything. I do speak to the child every day but father has told him to say I don't know to every question I ask. I have seen the father in town tonight and decided to ask him in person when I can see my son since there is no communication from him at all such as text replies or anything. He flew off the handle calling me every name under the sun in front of my oldest son and told me I just need to drop everything or he is going to run with my youngest son because he doesn't want to deal with me and doesn't have too. He told me that I am lucky enough to still be alive but all good things come to those who wait. Hopefully, I will be gone soon. What can I do to get my son away from this crazy man? I have filed a modification of custody but court isn't until November 8.