On the top of my head I think that the comments part is in your page.php and/or single.php. But there are plugins that adds comments by action and not by code in the template (eg: jetpack or disquss).
And as always when I say stuff like this, dont edit the template files directly since any changes will be lost when you update. Instead go and edit the page or post in question and disable commenting with the postoptions presented.
the image I use is not centered or completely visible on all devices
can you post a list of devices where the problem occurs?