WhatsApp Plus or any other fake whatsApp app you have been using is the reason you have been banned. WhatsApp doesn't like want people to use other clients for this. See here their warning about WhatsApp Plus:
"WhatsApp Plus is an application that was not developed by WhatsApp, nor is it authorized by WhatsApp. The developers of WhatsApp Plus have no relationship to WhatsApp, and we do not support WhatsApp Plus. Please be aware that WhatsApp Plus contains source code which WhatsApp cannot guarantee as safe and that your private information is potentially being passed to 3rd parties without your knowledge or authorization.
Please uninstall your application and install an authorized version of WhatsApp from our website or Google Play. Then, you will be able to use WhatsApp."
No one knows yet if you will still be able to use WhatsApp Plus after that period of the ban, but the smart thing to do is to now use the original WhatsApp.
We covered this issue here: http://www.techzim.co.zw/2015/01/banned-whatsapp-blame-whatsapp-plus/