Unalble to hide featured Image

Hi,
I have copied and pasted the code that was listed in another person with the same problem, but still nothing happened, featured image is still showing in single post, is there any other solution to resolve this?

the code I replaced;
.has-post-thumbnail img.wp-post-image, img.featured{ display: none !important; }

https://www.ads-software.com/plugins/hide-featured-image/