If it were a spirit of some kind coming into your sons beroom, why would it open a door? If I were you I'd question your son more on this.
Do you have children?
What did the man look like? What else did he say? Did the man touch you? This story to me sounds very worrying indeed. Someone earlier said what if someone else still had a key, I think a good idea would be to change your locks, and improve your houses security. Unless all this was a long time ago?
Your questions here were all addressed and resolved.
Like others have said, I urge you to keep an open mind and question everything. There are good things about the religion, but as you will find out, the majority of people on this website have been hurt by the organisation and the way it controls its people, by forcing them to shun all who are not Jehovah's witnesses, even if that includes their own families.
If you feel praying helps you, then I suggest keep praying, and look into other faiths. Also consider that maybe you don't need a religion to set you laws and restrictions, maybe you could have a healthy relationship with God and your family without anyone else telling you how to do it.
I wish you all the best in your searches, and just remember there is nothing more important than your own family, not even a God or a religion.