How to know wether the Phone Device is currently in call or not in iOS Native code or Unity C#?

Question

I am trying to build a Unity plugin that can detect if the Phone is in a phone call or not. I want to prevent the Game Video recorder during a phone call.

I write this Objective-C code and a corresponding C# class in Unity like this:

Objective - C plugIn
PhoneCall.h

#import <Foundation/Foundation.h>
#import <CallKit/CallKit.h>

@interface PhoneCallDelegate : NSObject
{
}
- (BOOL) isOnPhoneCall;
@end

the Implementation :

#import "PhoneCall.h"

@implementation PhoneCallDelegate

- (id)init
{
}

-(BOOL) isOnPhoneCall {
    CXCallObserver *callObserver = [[CXCallObserver alloc] init];
    for (CXCall *call in callObserver.calls)
    {
        if (call.isOnHold || call.isOutgoing || call.hasConnected) {
            return true;
        }
    }
    return false;
}

@end

static PhoneCallDelegate* delegateObject = nil;

// When native code plugin is implemented in .mm / .cpp file, then functions
// should be surrounded with extern "C" block to conform C function naming rules
extern "C" {

    BOOL _InPhoneCall()
    {
        return ([delegateObject isOnPhoneCall]);
    }
}

the Unity C# Class PhoneCallController.cs

using System.Collections;

using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;

public class PhonCallPlugin
{
    /* Interface to native implementation */

    [DllImport("__Internal")]
    private static extern bool _InPhoneCall();

    public static bool IsDuringPhoneCall()
    {
         return _InPhoneCall();
    }

}

then I am trying to call IsDuringPhoneCall() Method threw this Script

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PhoneCallController : MonoBehaviour
{
    void Update() 
    {
        if (Application.platform == RuntimePlatform.IPhonePlayer)
        {
            Debug.Log(" During a Phone Call : " + PhonCallPlugin.IsDuringPhoneCall());
        }
    }
}

And i tried to call the Device then Launch the app , but the Method always return False.

I dig more into the code and return the count of Calls and it turns out that it always returns 0.

Why does that Happen? And How can i know if the Phone is During a phone Call in Unity?

Thanks in Advance