You don't cancel interviews with such a short notice unless you're sick or have had a different very important incident that made your participation impossible.
By scheduling and cancelling because "your tasks at the current job accumulated" you showed them you are bad at planning and foreseeing the effects of your decisions and that you can't be counted on.
You are yourself to blame for the rejection. Of course, we all make mistakes. It's not the end of the world but try to learn from it.