Hey there, and welcome to Apple Support Communities, elask22!
From my understanding, you disabled Background App Refresh on your iPhone for all apps, however it looks like it’s being used by WhatsApp. I’d be happy to help!
Since you mentioned that it’s already disabled, I’d recommend enabling the feature for WhatsApp, restarting your iPhone and disabling it again. If it still occurs, Update your iPhone, iPad, or iPod touch - Apple Support after completing a backup of your data. Once complete, use Update apps or use automatic downloads - Apple Support to ensure you have the latest version of WhatsApp.
Let me know the results, and have a great day!