How can I achieve operator agnostic call barring? so, I've got a rooted Samsung G800F.

My objective:


The phone has access to mobile data (not WiFi). (Intended for
streaming Amazon and Youtube and maybe a bit of surfing or
tethering.) 
The phone can not be called. Ideally the phone can not call or get/send sms and install other applications. 
The calls do not get blocked. (They are intended for a second cell using the same
number/contract.)


What I tried so far and deem useless:


Call Barring (My operator does not support this.) 
Call Blocking (My
other phone has no chance to answer the calls.) 
Do not disturb/silent
mode (It could still be answered and the calls are still visually
signalled.)


What I'm trying now:
Fiddling around with the phone app.

And here I'm absolutely lost and hope you can lend me a helping hand.

So, I tried Titanium, but couldn't identify the correct app. I froze and killed some suspiciously sounding/looking ones, but calls still went through and the ringer went uninterrupted.

Next I installed "Root Uninstaller"
Here I found com.android.phone and had some partial success with killing this or some services. 

There are two problems though: 


I do not know what I'm doing. Not a clue. So, can you tell me what service to disable?
When I reboot the device it has problems and constantly displays an error message/is almost unusable.
(Falling under the "ideally"-category: can I just freeze some "Play"-App to prevent installation of messengers - relying on the phone number - and such?)


(Just FYI: I'm from Europe and might read and respond at odd-seeming times.
 I wanted to include the tag call-barring, feel free to add this.)
That's probably not possible at the moment, as you'd have to forward the calls using VoIP. This is way too complicated to implement on your own, as these features are already builtin to the mobile network.

Alternatively your MNO may have some USSD codes for automatic call forwarding, so you need to look if those are available to you. 

Unconditional Call Forwarding is usually activated with:
*21*[phone number]# and cancelled with ##21#. For other options, check the link.

Call Barring:


  If you wish to restrict calls that can be made or received by your handset then this is referred to as "Call Barring". All Call Barring codes are specific to your network, so you'll have to ask your service provider


Also check this