Is it possible to completely disable phone calling on Android? I've disable the built-in phone app but an a voice over IP app took its responsibilities, I killed that too, disabled notification and tweak everything I could find except for turning off the ringtone in the settings and the phone will still ring, except I can't answer because there's no app for phone calls!

When I receive a phone calls there's a lingering notif as usual I always delete it along with the millions other notifs Android gets nonstop--it's really annoying, I never tapped on it because it does nothing, I remembered however that this version of Android brings more stuff at the first tap. I spent the last two hours trying to remember my own phone number to call myself and bring up the notification, upon tapping it it let me to the system app Phone Call Management which is not blockable. I want to reinstall my VoIP app, it requires to have a ringtone so it can ring too; is there another way around this?

BTW, I also installed phone call blockers, but don't really help in here.

Thanks!
Try MTK Engineering kit. You can disable calls from that by turning radio off. Alternatively, use in dial pad *#*#4636#*#* and a window pops up. Now select phone information and scroll down to find the radio option. Now turn off the radio. Then you will not receive any calls. Otherwise you can use airplane mode as well.