How to stop wordpress from creating thumbnail

I try to save my server diskspace by stop wordpress from creating thumbnail when upload an image,

Set thumbnail size to zero in Setting>Media

Add these snipped to my functions.php
add_filter(‘intermediate_image_sizes_advanced’,’stop_thumbs’);
function stop_thumbs($sizes){

unset( $sizes[‘thumbnail’]);
unset( $sizes[‘medium’]);
unset( $sizes[‘large’]);
unset( $sizes[‘post-thumbnail’]);
return $sizes;
}

It doesn’t show thumbnail option when upload but still creating other files with different size in host.

Thanks for your help.