First I must say how disappoint it is to come all this way here simply to remove customer from my project/site/space or whatever it is called now.
Spent 3 hours on research to stop in the same problem, I can't find out why its not possible to remove a customer.
Created some random names and e-mails for testing and now I want to delete then. But the is no delete button there, I can remove organizations which I have already done, but I can't get rid of these customers.

https://community.atlassian.com/forums/Jira-Service-Management/Removing-Customer-JSM-Free-Tier/qaq-p/3134630
This post explains how to delete from the Admin page, it's said to go under products. Well I can't find where this products is as well.

Some other places say to go under Admin/Users. Well, that does not help either.

I'm sorry If I'm being rude, it just seems so basic that anyone would need to manage customers that I can't believe its so difficult to achieve