You can use the block function to prevent specific users from communicating with you.
1. To block a user, you need their ID number, not their user name. To find their ID number, click on their username or profile picture from anywhere on the site to open their profile page.
Their user ID is displayed on the right hand side of the page.
2. Choose "Settings" from the navigation menu.
3. Choose the "Other Settings" tab.
Under "Block user (only viewable by you)", and enter their ID number.
4. Click on "Save"
Users blocked in this fashion will be unable to communicate with you.