For inherited parent theme you need to add Template lines in child theme. Please read this https://codex.wordpress.org/Child_Themes
/*
Theme Name: Twenty Fifteen Child
Theme URI: http://example.com/twenty-fifteen-child/
Description: Twenty Fifteen Child Theme
Author: John Doe
Author URI: http://example.com
Template: twentyfifteen
Version: 1.0.0
License: GNU General Public License v2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
Tags: light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
Text Domain: twenty-fifteen-child
*/
Here “Template: twentyfifteen” is important to call parent theme. Please check this in your child theme.
Also you can use this plugin to generate child theme. https://wordpress.org/plugins/one-click-child-theme/
I hope this will help you solve your problem.