Make sure that you are using the latest version of WhatsApp Messenger from the APP store
Restart your Vodafone
Make sure that data is enabled (Android Settings== > Wireless & networks ===>Mobile
networks) and enable data.
Contact your mobile provider and make sure your APN settings are configured correctly.
Delete and reinstall WhatsApp (Note: This will erase your chat history. Be sure to run a manual backup beforehand by going to WhatsApp > Menu Button > Settings > Chats and calls > Back up chats or Chat backup > Back Up.