However, if you open the linked page and view the comments at the bottom you will find most of them are requests to close accounts. You could try posting a request in a comment there, and contact support if that doesn't work.
https://support.cex.io/hc/en-us/articles/201516097-How-can-I-delete-my-account-from-CEX-IO-
In order to get your account deleted please contact the support team by sending a ticket and your request will be processed ASAP.
Please note that according to our Privacy policy and in accordance with our record keeping obligations we will retain Accounts and Personal Information for at least a period of five years after they are closed by Members.