Harrasment

I have arrangements to pay R100 pm which I am doing. Each month I am called by Valerie to either asked me if I paid after payment has been made or when is the next payment. It is annoying me as I am harassed and each time they phone they charge you in other words R50 will go off your account and you will be paying on this account till the day you die. This is not acceptable. I asked her on previous occasions if I paid. LEAVE me alone. And they still harassing me.