Custom Function -> Page/Post functionality

I have been playing around with the Contact Form 7 for a few days.
What I am trying accomplish is the following

1) Setup up a form
2) When clicking submit I “enter” my custom php function where I have hooked one of these events
* add_action( ‘wpcf7_before_send_mail’, …
* add_action(‘wpcf7_mail_sent’, …
* add_action(‘wpcf7_mail_failed’, …
3) In this custom php function I want to do some handling of the data filled in by the user. Like calculations and such.
4) The result needs to go back to the user. I was thinking through a simple GET like http://www.mydomain.com/ResultPage/?result=FooBar
This way I can present it nicely. (the present page is working)

What I have succeeded with so far is the first 3 steps, but the fourth one I can’t figure out.

I have tried all kinds of ways, like these two
* Changing the posted data (which did not have any effect)
* Doing a wp_redirect (which broke the form, it wouldn’t “complete”)

Any help will be much appreciated 🙂

https://wordpress.org/plugins/contact-form-7/