Method 1 (Sure Fix but requires root):
Install a file manager like Root Manager
Browse to internal storage android/data/com.whatsapp
Delete the com.whatsapp… folder
Now install whatsapp from Google Play
Method 2: Removing Junk Files via Cleanmaster
Now run Cleanmaster , search for Junk files and clean them. (Make sure to uncheck important files that are detected as Junk files by Cleanmaster)
When all fails backup all your apps and data and factory reset your device.