close/delete my wordpress site

This is between you and your hosting company. If you have a site you want gone, tell them to terminate your hosting agreement.

if your site is on wordpress.com, you need to contact them directly. Due to the differences between the free hosted blogs offered at wordpress.com and the self-hosted and self-installed version of WordPress supported here, you should probably ask WordPress.com Support instead.

Just got this email on how to do this today from Elegant Themes.com