Incoming calls not ringing on iPhone 6

Report
-
Hello,

Incoming calls not ringing except when I am in WhatsApp app. I do get miss call message when I open the app. I have tried all the possible setting options except “reset phone”. I have updated WhatsApp and IOS. In case I keep the screen on and WhatsApp app is on the screen, I do get the ring.
Please help

System Configuration: iPhone / Safari 12.1.2