What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Thank you for contacting us.
You can use our unique submission feature to block multiple submissions from one system of one IP address by setting the "Loose check" or "Strict Check" respectively. Inside of this article you can see how to set Unique Submissions on a Form: http://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form
You can also use our unique question feature to prevent from submitting duplicate submissions. Example: You can set one of your forms question (like cell number or email address) to be a unique question. This will not allow a user to use the same cell number or email address to submit your form. Here is a guide to help you: http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question
Hope this will help. Let us know if you need further assistance.