Severe and continuous harrasment by so called CellC operators

I have been consistently harrased on a daily basis on my private phone number and my work number (which I have not shared out with any one as it is for work) They call me from various numbers indicating that they would like to discuss my CellC contract (of which i do not have). When requesting details of this so called contract i get various responses depending on the caller, either they cut the call, be rude and indicate the details they called, or demand that i provide them with all my personal details. I have sent emails to complain and ask for this harrassment to stop but to date it has just increased. I managed to get 6 numbers of this so called contract and then the call was cut before it could be concluded. I have received an sms with not much details also indicating I have been handed over but nothing formal with any details to date. How on earth can i get this to stop or that they will share what they have so that i can take legal action.