Turning off comments in Discussion does not affect content that was created prior to our change. The following is a quick way to make sure all our content has comments turned off.
1. Go to Posts
2. Find how many Published posts you have
3. Click on Screen Options in top right corner and add the amount of posts the click on apply
4. Click on the checkbox next to title (this will select all the posts on the page)
5. Go to dropdown and select edit and then apply
6. Go to comments drop-down and select Do Not Allow
7 Click on the Update button on right hand side
Now all your current posts will have comments turned off.