Is there anyway I can prevent my form respondents from getting a jotform marketing popup window?

A respondent told me that when he completed the form, he got a popup window that asked him to establish his own JotForm account. Is there anyway we can prevent that popup window?

We are currently using the free JotForm account because we have less than 5 forms.

We are using the form on an internal page, so I can't provide you a link. The popup window only occurs occasionally, so I do not have a screen shot for you either. I'm really sorry. I know that might make it more difficult.

This is the thank you message shown after a form is submitted: 

If you do not want to show the JotForm branding then you could upgrade your account and disable the option on your account settings: 

You may also redirect your users to a different page, this guide will help you to do it: https://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page 

Hope this helps.