Update to plugin breaks wordpress admin

I previously had this plugin installed on my site and everything was working correctly however after updating this morning it has broken the backend of wordpress logging this error in the server logs:

PHP Fatal error: Uncaught Error: Call to undefined function is_plugin_active() in /var/www/html/wp-content/plugins/refer-a-friend-for-woocommerce-by-wpgens/includes/class-gens-raf.php:166\nStack trace:\n#0 /var/www/html/wp-content/plugins/refer-a-friend-for-woocommerce-by-wpgens/includes/class-gens-raf.php(76): Gens_RAF->define_admin_hooks()\n#1 /var/www/html/wp-content/plugins/refer-a-friend-for-woocommerce-by-wpgens/gens-raf.php(45): Gens_RAF->__construct()\n#2 /var/www/html/wp-includes/class-wp-hook.php(286): run_gens_raf('')\n#3 /var/www/html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array)\n#4 /var/www/html/wp-includes/plugin.php(453): WP_Hook->do_action(Array)\n#5 /var/www/html/wp-settings.php(327): do_action('plugins_loaded')\n#6 /var/www/html/wp-config.php(89): require_once('/var/www/html/w...')\n#7 /var/www/html/wp-load.php(37): require_once('/var/www/html/w...')\n#8 /var/www/html/wp-admin/admin.php(31): require_once('/var/www/html/w...')\n#9 /var/www/html/wp-admin/themes.php(10): require_once('/var/www/h in /var/www/html/wp-content/plugins/refer-a-friend-for-woocommerce-by-wpgens/includes/class-gens-raf.php on line 166

I have since removed the plugin from the site but this basically makes the plugin unusable.

Thanks,