By enablinig this plugin, it prevents double clicks when Contact Form 7 is still submitting the form that causing the multiple same submissions coming through.

For Contact Form 7 version 4.9 or above.

1. Download this plugin thru this repository - click "Clone or download" drop down then click "Download ZIP" and save it.
2. Within your WordPress dashboard navigate to Plugins -> Add New then click "Upload Plugin" then choose the zip file that downloaded previously.
3. Click "Install Now".
4. Once plugin installed, activate it thru Plugins page within your Dashboard.