When you click the little Comment balloon at the bottom of your story, you'll see a list of comments. Each comment has an ellipsis like this:

...

Click that, and for the comment you wish to hide, choose "Hide Comment"

Readers of your story will no longer see that comment. It's really the easiest way to deal with trolls. I don't even block them. I just let them keep attempting to comment, and I hide the comment.

I've looked at my stories in incognito mode in Chrome and confirmed that it is not just hidden for my account.