The title of this thread caught my eye because I've had many problems with the telephone company in recent months, although none quite like the one described here.
I've read all of your posts, ITK, and it strikes me that what we may have here is a failure to communicate. That is, I suspect the people you've talked to didn't understand your problem because you keep using the wrong word to describe it.
You say that someone is listening to your conversations. What you should be telling the phone company is that you are hearing other voices on your phone. Unless one hears another person on the line, one has no way of knowing that someone is there and possibly eavesdropping on the conversation, so someone simply claiming that another person is listening to their conversations without additional information might be dismissed as crazy. But you say you DO hear this mystery person, that he has cursed at you -- it's extremely important that the phone company know that.
Call 611 (the repair number for most phone companies) and tell them that you have heard other voices and noises on the line. Don't make a big deal out of it by claiming that someone is deliberately spying on you. Just ask to have the line checked and repaired. As others have suggested, it may be something as simple as a problem with wires being crossed in the equipment, which can be easily repaired once the problem is located or by simply rewiring your connection. That's something that the phone company understands and can address.
I sincerely hope that your problem is fixed soon.