How do I get rid of telemarketing phone calls at my business?

[Msknowitall I]

I run a Dr's office. And all day long, I get various telemarketing calls, for crap they are selling or janitorial services or whatever else B.S, they are selling. These are people or services that I have never inquired about in any way. I have to run out of a patient room, meetings, important things, to answer the call, just to find out its a telemarketer. I feel like telling them to go F*** themselves. I know there is a Do Not Call list for home/personal phone#, but what can I do about the business calls? I have repeatedly told them that I am not interested and to not call me anymore, but they get an attitude and will continue to keep calling even more. They call from blocked/restricted phone#. How do I report them for harrasmant if there is no phone#. Any ideas on how to handle these telemarketing calls?