How to block the strange numbers?

I have an iPhone 5. Recently, I've been getting these calls from random numbers. When I answer, they just hang up. I've gotten like 7 calls just today. It's creeping me out and I want the calls to end. Is there a way to block calls like this?

I use an Andriod phone but even if I get into the settings/phone/calls/unwanted. It does not help much. Reason, the sender usually a marketer, uses a different code when calling you. It only work if you are blocking very specific numbers for people you know. Besides, it will drain your battery if this function is switched on.

You can block that annoying number in the phone book setting in your phone. Or you can get info for every phone number you didn't know by using reverse phone number lookup service online so you report it on the police.