can you block private number from contacting you?

I have an iPhone. Is there any way of doing this or do I have to contact my phone provider?
I've been getting regular calls from a private number. They ring me multiple times during the day, at random hours, when I answer, no one says anything, I can't even hear breathing, it's just silence as if they have mute on, I say hello then they hang up in exactly 10 seconds. It's getting annoying and I have no idea who it is.