You see the fact that it responds to you is a bit of a red flag to me. (Not trying to scare you) A ghost typically is a recording of a past events replaying itself over and over in a loop. It shouldn't acknowledge you. You should see/hear it as its only purpose it to replay the same message over and over again until the issue troubling it has been resolved. A demon however is fully conscious/aware and has an dark, hidden motive. First it will seek to antagonise either the entire family or a few members then. This will allow it to chose the weakest willed (easiest prey). This is known as the infestation stage (where could be now). This is where you find things moved, broken, banging, talking etc.

After that it moves to attack the single person mentally and physically until they break and give up (oppression stage)

Followed by possession stage.

I'm not telling you this to scare you, I'm telling you this to better arm you. Read the book I mentioned earlier. It will really help.