They are a collection agency it seems. I used to work for one so let me clear up some misconceptions I've seen.
-They are probably going to call when you're at work, they don't know your schedule, all they have is a number to call. If you answer and tell them to call at a better time (give them a specific one), then they probably will.
-They are not going to tell you exactly what the call is about until they confirm who you are. This is just the way it is because of federal laws.
-If you tell them they have the wrong number for the person they are calling for, a collection company will usually accept it at face value, make a note on the file, and move on to trying to find the correct number to reach that person.
-They should stop if you tell them they have the wrong number, if you tell them not to call anymore, or if you talk to them and find out it's a bill you know nothing about; tell them you aren't paying it, and they should stop calling. If they continue, they are in violation of the law, and can be reported.