Advo,
I hear you! People say those things, because they are ignorant. But you should never doubt that Jinns exist, there is a whole verse in the Qur'an about a group of Jinn who came to the Prophet (saw) and became Muslims.
These encounters are not common, but they happen! And when they do, they can have bad consequences. The Jinn are more than us in number and technologically more advanced according to ahadeeth. They have Muslims and non-Muslims. The non-Muslims are greater in number and very harmful.
Our weapon against them is the Holly Qur'an, their power is nothing against us, if we don't follow them.
I heard all sorts of stories about them growing up, I doubt it was true though!
