How can I get them to stop calling???

I continue to get phone calls from this agency on my answering machine.I have tried to call the 1-800 number they have given in the message to remove my number from their system as there is nobody here by the name they are trying to track down.They just don't get it and continue to harrass me with these irratating messages that are on my machine.It says in the message that," if you don't hang up that confirms that this is the person they are trying to reach." Obviously my answering machine will continue to stay on the line with them until they hang up.I have enough stress in my life of my own, I am very sick and tired of trying to get it through these peoples heads that the person they are trying to reach does not live here. If they would simply look in the local phone book for this area they would find the listing for this person as that is what I did. How in the hell did they get my number and what will it take to make them realize that they will never contact whom they are looking for by calling me? It is just a message on my machine but I am getting very angry, irratated and frustrated that I cannot physically talk to them and drill it into their heads I am not who they are looking for leave me alone!