Threaten me?? we'll see about that......

I'm sick and tired of this company. I cannot believe the nerve of these people, I've made arrangements to pay off one of my outstanding accounts, which I have committed to paying as agreed. I have pay as promise religiously and have not missed any payments thus far however, I receive non-stop calls from them, harassing me about a payment that's already been done and never missed and then yesterday they have the nerve of sending me a threatening email telling me if dont contact them soon additional cost will be allocated to my account. I MEAN ARE YOU ****ING KIDDING ME!!! who are you? what the **** is you problem. I sick to death of these people. the best part is, I call in to try and sort this out but the operator starts raising her voice at me and then expect me not to get upset after that the phone gets up down in my ear multiple times, I ask to talk to someone in charge with the promise I'll get called back but nothing comes from it. I WILL NOT PAY A ****ING CENT FURTHER. I'm going to get legal aid and I will take them on head on. I'm done with companies like this thinking they can do to people as they please.