I think you have to work on figuring out why it is so important that you want to call him.
What do you get from calling him, and find other things that are more important than calling him.
I was in the same boat as Anvil my doc was Meth and my dealers number was engrained in my brain. I couldn't remember my middle name, where I put my keys, or what I was even doing, but any time of the day I could remember his number, and as soon as I started to forget it, out of the blue it would pop up out of the blue, in a bill, on a piece of paper, he'd call, whatever.
I think just like an addict it just, best thing to do for yourself is work it out, figure out what is going on inside of us,
lol, I had forgotten it that number but writing this post, it just now popped into my head, iit's been over three years since I've called him.
In the end we have to learn to make better choices for ourselves if we want a better a life. Otherwise if I had "Just forgotten it" who knows what my decision may be.
Just my opinion and/or what worked for me.
Good luck to you with whatever ends up working!!
:ghug