FaceTime audio option greyed out, whilst FaceTime video call is working

I have iPhone 11 (Dual sim) HongKong model, my FaceTime audio option is greyed out and only video FaceTime calls are possible. I have done all the remedies, tried activation of FaceTime with different Apple ID, reset all settings, reset network settings, even factory reset, also tried clean install of iOS 13.4via iTunes and set it up a new phone. No luck. ☹️

Can anyone help please?