Magento 2. Custom Form. “FormKEY” and form validation is not working properly

I have a custom form that trigger a email. But I’m being attacked by some bot.

I’ve added the form_key in my form but the same key can be used N times and the validation is not working properly.

How can I prevent this?

<form action="<?= $this->getUrl('module/Ajax/myController') ?>" method="post" name="myForm"id="myForm" data-mage-init='{"validation":{}}'>
    <input name="form_key" type="hidden" value="<?= $block->getFormKey();?>">
    </form>

And my controller have this validation:

 if (!$this->formKeyValidator->validate($this->getRequest())) {
            $resultJsonValues['message'] = [
                'msg' => 'Invalid form key, please refresh.',
                'error' => true
            ];
            return $resultJson->setData($resultJsonValues);
        }

So if I go to Network tab in DevTools and copy/paste the request sent by the form in a new tab the validation does not work and continue with the submition with the same key.

How can I prevent this?

Thanks in advance.