why do I get unknown calls and when I answer?

the call no one answers, it's like a dead call?

------- could be a stranger… or hand-off/cross wire issue between 2 calls gone wrong in the node of the nearest twoer and your phone just happened to get it.

This happens almost everyday. Is it a way to eavesdrop on me somehow?

----- not really. Not by voice calls

Is there anything I can or should do to protect my privacy if it is someone snooping on me?

----- not really… other than blocking their phone number or calling police and filing harassment report

Does anyone have a clue what is happening?

----- nope… you can always call your carrier and report it, if it is a technical issue with a tower.

I don't know where you live or if this is something that happens in your country - but what's usually happen to me is that companies that are trying to sell you something calls a lot of people at the same time and the first that answers they talk to. And the rest they don't give a **** about. It's really annoying and all you can do is not to answer the phone I guess :) Or maybe you can block unknown phone numbers on your phone.