TJP, he will be able to see it now that he has a chance to sit with his thoughts instead of trying to manipulate you.
The way I see it, his calls are abusive. Scaring your mom half to death with threats of self-harm, whether it is the need to use or suicide, IS abuse and you are wise to say "enough and no more".
We don't need a front row seat to see and hear and listen to their addiction screaming at us. It's the worse seat in the house. "We" are not their solution. If he really wants help, even jail will assist him in finding it. If he doesn't, nothing you do or don't do will make a whit of difference.
Enjoy your day, wrap yourself in serenity and distract yourself from even thinking about him today. Maybe turn the ring off your phone too, or better yet, go for a nice walk in nature where you can't hear it if it rings.
Hugs from this mama's heart to yours.