Dropped calls etc

You are asking about two different things. Dropped calls can be for many reasons, and they can be a combination of things on both ends of the call, you or the caller.

As far as using FB, it could be that your carrier does not allow calls and data at the same time. However, when you mention nothing and they go to voicemail, you may have issues with your cellular carrier. They may need to replace your SIM, or you are in an area where service is not as strong. Do you see many bars in the signal strength for cellular?

Well, if anything, it could be an individual phone issue. I have an iPhone 11 Pro with AT&T, and I have to say that I cannot remember the last time I dropped a call. And AT&T, as a GSM carrier does allow for simultaneous call and data, which Sprint, a CDMA carrier may not be able to do unless you are on LTE. And I'm in a rural area, so I don't always have the best of signal. I cannot complain about my service or my phone.

You're welcome. It is possible. You can contact Apple Support if you wish and talk to them about the problem. Get Support

Not usually. It is usually a carrier issue.