How to block all outgoing calls? I want to block all outgoing calls regardless of who I'm calling since I have finished all my allowance.

I need a way to block all calls because I keep forgetting and I'll exceed my allowance. (I can use VoIP services instead).
Inspired by DrZoo's idea in the comments, if you have a rooted device and using Macrodroid, you can block all outgoing calls by following the steps below:


Open Macrodroid, click on Add Macro.
On the Triggers section, select Call Outgoing follwed by the contact(s) you want to block.
On the Actions sections, select Air Plane Mode On/OFF then choose Air Plane Mode On (you can choose to keep Wifi and Bluetooth on). Add the Wait Before Next Action and set it to 1 second. 
Add the Air Plane Mode On/OFF action, select Air Plane Mode OFF.


The image below illustrates the macro when completed. When you try to make a call, the air plane mode will be on, forcing the dialer app to stop the call because there is no connectivity. After 1 second wait, the air plane mode will be set to off, restoring connectivity.

Disclaimer: I am not associated with Macrodroid developer(s), only a user.