Sorry your having issues with your s9.
First thing I would recommend is to go to settings and scroll down till you see apps. Click on this and look for the app, they're listed in alphabetical order so you'll have to scroll to the end of the list of apps on your phone.
Click on WhatsApp and then click on storage location which should be internal.
Now clear cache then clear data.
Once that's done back space and first force stop the app then disable it.
Now do a hard reboot by holding the power button down until phone starts to reboot usually 5 to 10 seconds.
After reboot is complete go back to settings, apps, WhatsApp and reenable WhatsApp.
This should resolve your problem.
If not let me know as there is a little more complicated other options. But I recommend you try this one first.
Good luck to you.