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Unfortunately, spammers are indeed quite hard to stop, they can use automated scripts to replicate an actual submission, they can also use tools to have a list of proxies to constantly change their IPs.
First of all, as I have checked your form on your website, I have seen that you do not have any captcha to avoid spams. I recommend you to add a captcha to your form as you can see the following document: https://www.jotform.com/help/205-How-to-Add-a-CAPTCHA-field
You can also add Google Recaptcha Widget to your form as you find it at the following link: https://widgets.jotform.com/widget/google_recaptcha
Furthermore, what you can do is you can use is a drawing captcha. Here's the link: https://widgets.jotform.com/widget/drawing_captcha.
This one is much harder to pass, although the Google reCaptcha should already be enough.
Moreover, you can use an email verified. With that, it would be an additional step for them. First, they'll need to use a valid email address, then make an actual verification of it. Here are the email validation/verified widgets that you can use:
It is also possible that the website page where the form is embedded is actually the one being used to send the spams. Was your form embedded on your website page using the form's full source code? If you have used the full source code and it was not properly secured on the website page, then the spammers might have found a security hole or a bug that they are using for spams. If this is not the case, then spammers are just either doing an automated way of spamming or they are manually doing it. Either way, the email validation/verifier should slow and stop them eventually.
Finally, you can set unique submission on your from which is being spammed. Please check the following guide for this: https://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form.
Please try some of them in order to avoid being spammed.
Thanks in advance.