JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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.
Though it is not possible to block a specific user from filling out your forms, it is possible to set up unique submissions for forms:
Or a unique question:
This way, they would only be able to fill out the form once. This would also apply to other users attempting to fill out the form.