Hello
There are some questions that tried to ask the same, but I can’t seem to find the answer. It will be great if you guys can help me out. I came to notice this some days ago that I had made an account on codechef a year ago which I don’t use anymore. Codechef administrators, can you delete it?
Try sending them email : feedback@codechef.com
(Contact Us | CodeChef)
They would surely block your old account asap atleast… 
Rest you can read it here : How to delete my CodeChef user name / account - help - CodeChef Discuss
Codechef don’t support deleting an a/c.
All the best…!
you can email about this matter to codechef