Hey.
This really solved the issue! Thanks for that.
(For those who are interested. I deactivated all my plugins, and then reactivated them, now the Contact Form 7 is working just fine!)
One last question:
Is there a possibility to teach the text boxes to automatically resize? Because on the mobile version of my page, the boxes are way too large :/
Screenshots:
http://dj-thisa.com/IMG_1647.png
http://dj-thisa.com/IMG_3000.png