Jetpack comes with a built-in contact form which is activated by default when you install the plugin. This means that when you use the shortcode contact-form on your post or page, you will get Jetpack’s contact form instead of Clean And Simple. This is because both plugins use the same shortcode to display their forms. To resolve this conflict you must do one (or both if you want to) of the following things:
Deactivate JetPack’s Contact Form.
Go to the settings page for Jetpack by clicking the Jetpack link on the left hand side of your admin screen. Scroll down until you get to the Contact Form section and click on ‘Learn More’. This will reveal a ‘Deactivate’ button for you to click.
OR Use a Different Short Code
From version 4.1.2 onwards the Clean and Simple Contact Form provides an alternative shortcode for you to use. To use it simply place [cscf-contact-form] on your page to implement the form instead.