WhatsApp is just an internet-app, all that proves is that your phone has a working internet connection. It therefore follows that WiFi-calls at least, should work. These don't use apps and you make or receive the call entirely as normal using your phone's dialler.
Does your phone show the on-screen WiFi-calling indicator?
Given it's been a few days since you had these symptoms, ensure you have restarted your phone and toggled flight mode.
