Multiple card transactions from one user

I need some urgent help with an issue please. We have a customer who filled out our standard form and paid by credit card direct from our registration jotform. She then contacted us to say she had been charged twice, some 13 hours apart. Subsequently she has been charged twice more 15 mins apart for the same thing, so 4 times in total. She claims she only submitted the form once. From our end we can see the following:

There have received four identical submissions of the same form from this person (each time her credit card was charged). Three of these (including the first) were from the same IP address, which is consistent with the customers location. The third is from a different IP address that appears to be from a mobile device from the same country.

I have currently deactivated the form while trying to get to the bottom of whether it is a form fault, or something from the customers end. She has been suggesting that she will have to report it to the fraud office, so I'm wondering if there is something underhand being actioned by the customer themselves... especially given that 2 different IP addresses have been involved. I have refunded the extra payments but am being stung credit card fees, so need to get to the bottom of this. Any assistance greatly appreciated.

Most likely your user did not close the Thank You page once the form was submitted for the first time. Later on the Thank You page was re-loaded multiple times which caused the duplicate submissions. Considering that one submission is from a different IP address, I assume that your user used a mobile device to submit your form. 

You can prevent duplicate submissions, with Unique submission and Unique question features. 

How to Set Unique Submissions on a Form

How to set Form Limits Based on a Unique Question

Please enable on of this features on your form, to prevent duplicate submissions. If the same issue happens again, while one of the features is enabled, let us know and provide us the link of your form and the IDs of duplicate submissions.