When I am on a call on Messenger, how to avoid being disturbed by a WhatsApp call, and vice versa?

I happens too often. I am calling with somebody on WhatApp, then suddenly somebody else calls me on Facebook Messenger, or the other way around. I have a Samsung Galaxy S9. How can I set things up, if I expect a WhatsApp call, so that Messenger won't disturb? Making the Messenger caller believe I am not there. And vice versa also.