Here is a template for corresponding with a predatory journal’s editor to request for article withdrawal.
The template may be adapted as needed to suit your circumstances. You and your co-authors are advised to save copies of all your correspondence with the predatory journal.
Dear EDITOR’S NAME
I am the first / corresponding author on the manuscript [title] (Reference Number: [number]) submitted to the journal [name of journal]. I am contacting you requesting that you withdraw my manuscript, remove it from your server immediately, and never publish it in the future.
I and my co-authors hold the copyright to this work. None of us have transferred our copyright to [name of publisher], nor have we signed a publication agreement that gives you a license to publish our work. Therefore, should you publish our work you will be in violation of our copyright.
I have no intention of paying a withdrawal or publication fee, and I have no means or mechanisms in which to do so. You do not have the legal authority to post my manuscript on your site. I am again requesting that you withdraw my manuscript from your servers immediately and never publish it in the future.
I expect you to follow up with me via email with your explicit acknowledgement of this request. If my work remains on your site, I will find it necessary to enforce my request through additional means.
Sincerely,
YOUR NAME
Source: https://uark.libguides.com/WritingPublishing/Predatory
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Beall, J. (2016). Dangerous predatory publishers threaten medical research. Journal of Korean Medical Science, 31(10), 1511-1513.
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