How to Block a call when first call is ongoing?

Question

I have created an application for call blocking which is working fine but it's stuck in one scenario:

Scenario: When the first call is ongoing(user talking with the first caller) in between second caller call to same user & that new caller is in my Blocklist when my call blocking logic runs both calls ended immediately.

In the above case, I want to end call of second caller only. How to achieve this?

Is there any way to identify & block the particular call?

Here is my call blocking logic:

 TelephonyManager telephony = (TelephonyManager) context
                    .getSystemService(Context.TELEPHONY_SERVICE);
            String s = telephony.getClass().getName();
            Class c = Class.forName(telephony.getClass().getName());
            Method m = c.getDeclaredMethod("getITelephony");
            m.setAccessible(true);
            ITelephony telephonyService = (ITelephony) m.invoke(telephony);
            telephonyService.endCall();

Thanks in advance.