No sound during phone calls

My iPhone 7 plus has no sound during phone calls. Nothing comes out of the speak and the loudspeaker option is greyed out so I can't even use that. Occasionally when the sound does work, the other person cannot hear me either. As videos and calls via WhatsApp and other applications , are working job, there is sound in both way in and out call ,

my problem only during normal mobile calls

• If you have distorted Sound issue on your iPhone --> If you hear no sound or distorted sound from your iPhone, iPad
• If you are not able to hear the other person, click this...>If you can't hear a person on a call or voicemail or if the sound isn't ...
• If you only hear through speaker phone mode --> If your iPhone is stuck in headphone mode - Apple Support
• If the other person is not able to listen to you then please click this--> If the microphones on your iPhone, iPad, and iPod touch aren't ...
• If the above options do not mitigate the issues then Contact your carrier and then Contact Apple Support