vidisic

Solution required changes in wordpress core files, which is not recomended.

If you want to use Facebook Comment, you have to disable possibility to comment on your board. To do it, simply connect to your FTP serwer,
enter wp-includes folder, find file comment-template.php, then
find:

<p class="form-submit">
							<input name="submit" type="submit" id="<?php echo esc_attr( $args['id_submit'] ); ?>" value="<?php echo esc_attr( $args['label_submit'] ); ?>" />
							<?php comment_id_fields( $post_id ); ?>
						</p>

and replace with:

<!--p class="form-submit">
							<input name="submit" type="submit" id="<?php echo esc_attr( $args['id_submit'] ); ?>" value="<?php echo esc_attr( $args['label_submit'] ); ?>" />
							<?php comment_id_fields( $post_id ); ?>
						</p-->

next find:
<p class="comment-form-comment"><label for="comment">' . _x( 'Comment', 'noun' ) . '</label> <textarea id="comment" name="comment" cols="45" rows="8" aria-required="true"></textarea></p>

and replace with:
<!--p class="comment-form-comment"><label for="comment">' . _x( 'Comment', 'noun' ) . '</label> <textarea id="comment" name="comment" cols="45" rows="8" aria-required="true"></textarea></p-->

This way, you will hide comment form field and comment submit button, so bot will not be able to paste comment and submit it.