I have tried this code
$listId = 'xxxxxxxxxxxx';
//Mailchimp instantiation with Key
$mailchimp = new \Mailchimp('xxxxxxxxxxxxxxxxxxxxxxxx-xxx');
$mailchimp->from('xxxxxxxxxxxxxxx');
$mailchimp->reply_to('xxxxxxxxxxxxxxxx');
$mailchimp->to($email->email);
$mailchimp->subject('x');xxxxxxxxxxxxx
$mailchimp->message('<html>hiiiii</html');
$mailchimp->set_header('Content-type', 'text/html');
$mailchimp->send();