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I did test your form and after the submit button was clicked, it shows a page with heading "Form Closed". Please check the screenshot below:
It seems you have set "Custom URL (Thank you)" in your form which is redirecting to to FormCentral page after the form is submitted. Please check the screenshot below:
Please change the "Custom URL" of thank you page of your form and that should solve your problem. The following guide should help you: https://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page
Instead of redirect users to different page, you can also show the default thank you message or custom thank you message as well. The following guide should help you: https://www.jotform.com/help/211-Setting-Up-the-Thank-You-Page
Hope this helps.
Do get back to us if you have any questions.