Silence the user
Silenced users are prevented from creating new topics, posts, flags, or PMs on the site. They are still able to complete other actions, such as “liking” posts, reading topics, replying to PMs, etc. Additionally, they can communicate with moderators via PM, so you can continue to communicate with them to try and address the behavior.
Suspend the user
Suspended users are prevented from logging in, and thus from completing any actions on the forums. A suspension is the strongest possible recourse you have for a user and should be used sparingly. Like silencing, suspending a user is done from the user’s Admin page. Like silencing, suspensions are for a specific period of time. You may want to suspend the user for a short period of time first, and if the user returns and continues the behavior, increase the suspension time.