In Android Pie, there is an official way to block the incoming calls using endcall() function in TelecomManager,

https://developer.android.com/reference/android/telecom/TelecomManager#endCall()

To use this function you need ANSWER_PHONE_CALLS permission. This is categorized as dangerous permission, so you need to request this permission during runtime instead of adding in manifest file.

if (checkSelfPermission(Manifest.permission.ANSWER_PHONE_CALLS) == PackageManager.PERMISSION_GRANTED) {
    TelecomManager tcm = (TelecomManager) context.getSystemService(Context.TELECOM_SERVICE);
    if (tcm != null) {
        try {
            if (incomingCallNumber != null) {
                tcm.endCall();
                Log.d(TAG, "Incoming Call Blocked " + incomingCallNumber);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

EDIT: endcall() function is deprecated in Android Q (API 29), so you can use this method only in Android Pie (API 28).

My APP compile targetSdkVersion 22, In order to avoid dynamic application permissions，In order to avoid dynamically applying for permissions, but I cannot use endcall, the system prompts that there is no permission

android.permission.ANSWER_PHONE_CALLS

For the Android version less then or equal to 27, use the below code

iTelephony.java

public interface ITelephony {
    boolean endCall();
    void answerRingingCall();
    void silenceRinger();
}

 CallBlocker.java

        ITelephony telephonyService;
        TelephonyManager telephony;

                    if (Build.VERSION.SDK_INT <= 27) {
                        TelephonyManager tpm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
                        if (tpm != null) {
                            try {
                                Method m = tpm.getClass().getDeclaredMethod("getITelephony");
                                m.setAccessible(true);
                                telephonyService = (ITelephony) m.invoke(tpm);
                                if (incomingNumber != null && incomingNumbersList.contains(incomingNumber)) {
                                    telephonyService.silenceRinger();
                                    telephonyService.endCall();
                                    Log.d(TAG, "Incoming Call Ended " + incomingNumber);
                                }
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                    }