How do I fix calling issue on my iPhone 7?

Hi there, I am using iPhone 7 here.

I don’t know why, my iPhone didn’t fall off or get water comes in.

but, suddenly I cannot make the call. Whenever I make a call and receiver picking up its automatically disconnect. That’s when I am using Facetime Call

Different case on Whatsapp, when I want to make a call they say “can’t initiate the call. Please try again”

anyone can help me ?

[Re-Titled by Moderator]