Class ‘WP_Customize_Section’ not found Fatal error

I tried to install the Collect theme, but then I got the message:

Fatal error: Class ‘WP_Customize_Section’ not found in E:\HostingSpaces\Schreefstudio\schreefstudio.nl\wwwroot\wp-content\themes\collect\inc\customizer.php on line 30

Now I can’t change anything, can’t switch off any plugins for problemsolving and my site is offline!

In the custimozer.php on line 30 it says:

if ( ! function_exists( ‘abc_premium_features’ ) ) {
class Collect_Customize_Section_Pro extends WP_Customize_Section {
public $type = ‘premium-upgrade’;
public $pro_url = ”;

Do I have to add anything? Is something wrong with the theme?

Thanks in advance for any early solution!