Trying to insert a row from a Plugin

insert is not a static method. So you can’t call it like this: wpdb::insert(/*...*/).

You’ll need to do something like:

global $wpdb;
$wpdb->insert(/*...*/);

Or create your own instance:

$db = new wpdb('dbuser', 'dbpassword', 'dbname', 'dbhost'); // change these!
$db->insert(/*...*/);