Have you ever thought about filing a police report? How long has this been going on? If this infringes on verbal elder abuse which causes emotional harm or distress, you may also want to seek professional assistance from an attorney to see if legal action is necessary. You do not have to continue to subject yourself to such treatment. Your adult child may have an enormous amount of personal issues and is simply taking them out on you and probably trying to be very intimidating. The good thing is that your adult child is in another state so that physical contact is not available.
I hope that this has helped. If so, please ACCEPT so that I may be paid for my efforts. If you need further assistance, please let me know.