Hang in there Susan
It sounds to me like your son is turning up the intensity, hoping you'll cave in. You've taught him over the years that if he asks, whines, manipulates and behaves badly, then eventually you will bail him out of trouble. Now that you're not reacting according to the old pattern, he's confused and will try harder to get his way.
A few months ago there was a thread in PE about things to say to your difficult child when you are detaching. I suspect that you can find it in the archives.
What I would suggest is that you print out the list, go through each of the things your son has been saying to you, and pick out one or more responses that suit the situation. Even say the phrases out loud, so that they feel natural and comfortable. Then, when your son phones to ask for things, or make demands on you, you'll be ready with things to say.
It's really hard when you're trying to change old patterns, especially if you're caught off guard, or when your emotions are running high. By preparing and practising ahead of time, the detached answers will become second nature and will roll off your tongue automatically.
Think of it this way...you have fire drills at school when there is no real emergency, so that you, the other teachers and the students are familiar with the process. If there ever is a real fire, everyone will be ready and will know what to do.
Preparing a list of detachment answers ahead of time is like a difficult child fire drill. When your difficult child strikes the match, you will be ready and you will know what to do.
You've shown such progress and strength in your new approach to dealing with your son. Keep up the good work. You can do it.
All the best,
Trinity