Debt paid off 3 years ago - keep phoning

I paid off a woolworths account 3 years ago and Norman Bisset & associates keep phoning me. I have told about 5 agents and emailed all the information through to Fanaaz Fortunuin at their company, logged a complaint and asked them to draw a statement through Woolworths and see the lumpsum payoff. And all the agents keep saying is \Oh Okay"and as true as nuts I keep getting calls about the same matter. I need a manager to look at this matter and sort it out once and for all. """