Debt Colleting when there is not debt to be collected

Norman Bissets and Associates keep on sending me that they are going to hand me over for outstanding debt. I had called Vodacom legal to see if they had handed me over and they have not record of this. When i asked then please send a letter to this company to state Vodacom did not issue this collection they said they cannot as they do not have record of this. So what am i now to do , have this company on my back every 3 months or so or will Vodacom do something about this as the company states it is one Vodacom's instruction