Jehovah Witnesss is this true about your faith? This is a real question?

Why does the Jehovah Witnesses believers continue to use the name Jehovah? Haven't they read That God in the book of Jeremiah forbade the use of the name Jehovah? To whom are they witnessing for? is there a court case for Jehovah?for sure in Hebrrew there is no letter J so what happens next.