I have been struggling with this too. No matter what settings I use the default 1mb file size is still there.
I tried now to hard code the default file size in the plugin. And it worked right away with a 5 mb limit.
This is not a recommend method since it will be overwritten when the plugin updates. But as a testing method it was great because I could rule out any other problems.
The settings can be found in this file:
/wp-content/plugins/contact-form-7/modules/file.php