Blocking phone calls in Android before API 28

I have found code to programatically block phone calls in Android here, and the following code works:

    val telephonyManager = context.getSystemService(Context.TELEPHONY_SERVICE) as TelephonyManager
    val m1 = telephonyManager::class.java.getDeclaredMethod("getITelephony")
    m1.isAccessible = true
    val telephonyService = m1.invoke(telephonyManager)
    val m2 = telephonyService::class.java.getDeclaredMethod("silenceRinger")
    val m3 = telephonyService::class.java.getDeclaredMethod("endCall")
    m2.invoke(telephonyService)
    m3.invoke(telephonyService)

However, the above code blocks all subsequent phone calls until the device is restarted on API 26 and 25. All other posts on Stackoverflow give a similar solution to this.

Is there a solution for Android before API 28 that just blocks the current phone call?