False contract

In May 2015 I received a call from mtn to come and upgrade my contract no:A ********** with them and I declined the offer. Then few days later I received another call welcoming me to the upgrade and I immediately went to the store in rustenburg square and spoke to Maxwell who promised that they will resolve the matter after I gave them affidavit that I did not renew any contract. In October this year I got a call from Shamde at mtn and I explained the whole story and she asked me to resend all my docs which I did. I have now been getting threatening sms from Hammonpole that they are collecting debtors and my so called account has been refereed to them, is this a joke?? This has negatively affected my profile and I want it fixed immediately. Id no ********** 911087. I never upgraded any contract.