Hey KF,
the form is being resubmitted because browsers work that way :) you can notice on other websites that if you fill in a form, submit it, and then try to refresh the same page, the browser will ask you whether you’d like to resubmit the form. The only way to circumvent this that I could think of right now is to create a cookie each time a form is being submitted, telling it not to try to resubmit on page reload; however, the catch would be that the cookie is minimally valid for the duration of the session, i.e. until you close your browser and open it again, you won’t be able to send the form once more.
Sincerely,
Andrii / Satori Studio