How do you get them to stop

I get 5-6 calls a day for the past week - I don't answer numbers I don't recognize and they never leave a message..but this is harrassing...who are they?

please this number call me every 30min and i answer they say nothing i just don't want to call me anymore

this number constantly calls and i answer and they say nothing..i call back and all i get are beeps!