Why can't I see some submissions?

I have a user that contacted me checking that their submission of content and payment went through, but I can't see it. There's no record of a submission but they have record of the payment. 

Hi, thank you for contacting us.

Upon inspection of your form submissions, I could see 6 submissions marked as incomplete payments.

Perhaps it was one of these incomplete payments?

If you need further assistance please let us know. We will be happy to help. Thank you.