There was a white ferret (or we could say blonde ferret) at the door of your house, at that time someone rang your doorbell. And when you open the door there is a white ferret in front of your house, and there is a robe with the snake symbol (Slytherin robe) near the ferret. Ferrets are actually humans. His name is Draco Malfoy. He disguised himself as Ferret. He could have changed to his original form.