When you hit the submit button, a message is displayed on the top saying “email has been sent” indicating successful submission. The confusion is probably because the form is not reset and fields cleared out when the contact form is submitted. I have rolled out updates for some of my other themes to fix this and next update of Extinct will have it too. Meanwhile, you can use this fix –
For modifying the contact form, you need to modify the file framework/shortcodes/contact-shortcodes.php and for validation changes, pls have a look at line numbers 262 to 284 in js/main.js file.
For advanced contact form functions, I recommend you use Contact Form 7 plugin. It is easy to use and works well with this theme.