How to take down old site

In 2014 someone decided to create a dummy website of our organisation – without warning anyone and I asked them to take it down. When I recently did a search or our org’s name I found its still up under the yoursite.wordpress.com URL format.

I found the login details to the site but it seems to related to something else now and is empty.

How do I get the dummy site under the wordpress.com address taken down?

Thanks