That's a non issue.
You just cannot expect to be able to delete anything you post on the internet.
Even the great reddit with the awesome deletion feature cannot help you. You might be able to delete your comment there, but there is https://www.unddit.com/https://archive.is/https://web.archive.org/ and many others, where your comment will still be available.
Do you think about Reddit "undeleting" posts?
The reason for this is that your posts in privated subs make them disappear from your profile.
So when they go public again, they are there.