calling myTimer.cancel() won't stop the timer

Question

      private class MyTimer extends CountDownTimer{
       public MyTimer(long timeLeft,long timeInterval){
        super(timeLeft,timeInterval);
      }
      public void onTick(long timeToGo){
        //code to execute on every tick
      }
      public void onFinish(){
      //code to execute onFinish
      }};

I am trying to make an app using a timer above but calling myTimer.cancel() won't stop the timer. Pls help. The timer continue counting