I keep getting calls from an unknown number? Should I be worried?

I have an iPhone. Almost every call I've ever received comes in as the phone number, or the contact. I've been selling my car, so I've had a lot of calls from strange numbers lately. No big deal. It's all car people. But lately… I've started getting calls from something marked as "unknown".It doesn't show the number. I answer, say hello, no one says anything. A few seconds pass, they don't hang up but I don't hear anything. Then I hang up. I wasn't worried the first time. But this has happened at least 3 times in the 5 days. Now I'm getting a little concerned.

I figure it's NOT a telemarketer, because there's NO RECORDING or person. I also have no reason for anyone to be prank calling me--that hasn't happened since high school. I also figure this isn't someone calling about the car, because they would say something, or if it's a bad connection, call back.
I do however have an ex boyfriend who beat me up, and who I have a restraining order against, and pending legal charges. He's NOT allowed to contact me, and he's never tried to--he's been busy dating loads of women, anyways.

Should I be worried? Is there a way to find out who's making these calls?

Added (1). My phone number is NOT on facebook.

Will if you ever saw that one movie were a stranger is calling, and you don't answer it, because your too shy.end of story.

Try calling to company also ik you can block unknown callers if that helps. Or just change your number

If it shows up as unknown, don't answer it. It's probably somebody doing it as a joke. Happens to a lot of people who put their number on Facebook. Don't stress.

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