Reply received from the WhatsApp team..
"The WhatsApp app has been temporarily removed from the Windows Phone Store due to a recently discovered issue with how notifications are handled on Windows Phone 8.0 Update 3 (Lumia Black on Nokia Lumia phones). We are in the process of working with WhatsApp to resolve the issue as quickly as possible. Thank you for your patience and sorry for the inconvenience."
So, you need to wait till the application is made available once again
BTW, always 'search' before starting a new query.. There are already a few threads on the subject.. e.g. ***HERE***
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