I have to rely on my calendar app on my phone for remembering any event. Without it, I’m out of luck

Last time I went to therapist.
I only remembered at work. I tried to text him, but didn't get a response, and I really struggle with phone calls. I don't know why. It's even worse than talking in person for me.
Like, I'll go to some lengths to avoid phone calls.
My favorite is turning off VoLTE/VoNR/VoWiFi and 2G/3G leaving no way to connect phone calls.
OR, after 3G shutoff leave that on. On the other party's side the dialing will actually wait for the impossible handover, so they might not even blame my phone.
Possible outcomes (caller side):

1. (Common) "The person you are calling is not available at the moment."
2. (Rare) Silence until disconnect during dialing
3. (Legendary) "It has not been possible to connect your call."

I've also played around with conditional forwarding for this. On busy works for hang up. And my carrier seems to use a separate phone number for handling unreachable situation. Copy pasting it from "when unreachable" to "when busy" lets me pretend to be disconnected on demand. Now, it can still make people suspicious, as it usually doesn't ring before that message.
Another one is a test phone number, but unfortunately that one is considered a regular call, so it would cost others money, but "Welcome to CARRIER_NAME network" on infinite loop is funny too.

Oh wow, that is so me. That had better be under... yep, ADHD... yeah, that's in the right place.

It's worse when this triggers life-long anxiety about missing future appointments.

Worse still is when you show up a week early by accident, because you had it wrong in the other direction.

Happened to me a few days ago

Hey now, at least you remembered you had an appointment!

Good news is now your day is free

Even worse: It’s a remote session and you’re fifteen minutes late and the therapist calls you from NO CALLER ID and now it’s too late and you’re a no-show.