Double entries

Good day,

Could you please help me out with this plugin?
My client is receiving double entries when they submit the form.

When the form is submitted it will sent to info@kinderpraktijktheone.nl if I change it to my own e-mailadress taoufiq@fritsprint.nl I am not receiving the double entries.

Could you please resolve this issue?

Kind Regards,

click here for screenshot of double entries

The page I need help with: [log in to see the link]