It's hard, really hard, but eventually you need to come to grips with this thought:
You can't figure out the "why" of crazy.
And yet we all try, over and over again.
Remember, in his mind, regardless what he's done, he's not the bad guy in this story. So he'll be shocked, shocked, to discover you don't want to spend time with him, and take advice from him, or help him with phone numbers.
Speaking of which, you're not his secretary any more. He fired you from that. He can find his own phone numbers. If you're still in the same house, he can also do his own laundry, cooking, cleaning, and grocery shopping. You're fired, remember?
It's easier if you let his calls go to voicemail and respond via text. He'll eventually get the clue. It might take a while.
Since you're relatively new here, I'd like to recommend reading as much as you can in the healing library. The link is in the yellow box at the top left of the screen.