Click on your character pick top right,
click on your name at the top left of the new window
click on Preferences in the drop down menu
click on Users in the list on the left hand side of the window
You need to both Ignore and Mute the characters you want to get rid of. (Sorry I can’t remember what the difference is between the two settings just that I have the same people in both lists)
Oh and you can only block them for 3 (?) months at a time, 'cos 