Block next intent on new session

I built a session of 15 minutes, and custom action_session_start.

The problem here is that after starting a new session, if action_session_start detects that a previous form was left unfinished displays a message saying that you should start over, but also detects new intent and displays nlu_fallback response.

Is there any way to deny/block/skip next intent in action_session_start if that condition is met?

No one knows how to do this?