Unknown number

I am able to access a tool that tells me what number calls me, even if it is caller id blocked or restricted. Over the past month or so, I have started to get calls at LEAST 3 times a day from an Unknown Number that never leaves a message. I check and it shows that this is being generated from a computer on the internet and an unknown IP address. well, at least unknown to the tool I am using. This is REALLY starting to get annoying in that I am sure it is some random telemarketer that is power dialing millions of numbers. The thing that is annoying is that I am unable to block it at any sorta level