Under review since 9 months. Shall I send another email
Yes. The person you contacted in the editorial office is paid to answer queries like yours. It's exactly why the publisher employs them! Feel free to email again, just don't be abusive (they do not directly handling your paper, and they cannot act without the editorial board's approval). I also suggest against threatening to withdraw your paper, because it's likely to be ineffective. At most the editorial office can only forward your message to the handling editor, and they're likely to say "okay, you can withdraw it" especially since they're evidently having trouble finding reviewers.

As for what to write in the email, it's up to you depending on what you want to know. You could ask them to chase the handling editor again. It's also possible they might be willing to tell you more details about the manuscript's status: how many reviewers have been invited, how many reviews have been completed (if any), when further reviews are expected (if there are reviewers who've agreed to review but have not submitted), and so on.