Dropdown of user roles that depend on variable

1: $billing_company will return user billing_company whatever it is.
2: In $args you are supposed to put an array of user roles to fetch.

If you don’t know user role then you can use global var global $current_user; and $user_roles = $current_user->roles; to get all current user roles, so it would be

$args = array(
   'role__in' => 'his_company';  // string|array,
);

Check if it works?