How to delete/block a list of users contained in a CSV file?
You really don't need a CSV; all you need is the identifying column (e.g. mail or uid). To that end, you have one option  with the Bulk User Delete module.


  This module allows you to bulk delete users through the admin
  interface. You provide a list of email addresses, one per line, and
  the users are deleted using the batch processing API.


With this module, you can grab your mail column to feed into the interface to bulk delete.