Trouble submitting a payment

I have two pending submissions from the same person.  When will I know if this person's payment was received and if they paid twice for the same event?

Pending submissions/Incomplete payments are abandoned payments. You can mark them complete if you received their payments from another form or through a check offline. To understand more about the pending payments, please check this guide http://www.jotform.com/help/135-How-to-View-Pending-Submissions

If they already have made a successful submission in your form with a payment, you can delete the ones on the pending submissions list.