Cell C contract ****!!!

I am been harassed by Cell C and some stupid collections company regarding a none payment of a sim contract that I cancelled and had been debited on the said month. I received a message stating that my contract will be successfully terminated on 14/10/2021 as was stated by the consultant over the phone, to my surprise I have been receiving calls from a collections company since December that my account has been handed over by cellc, I have called Cell c countless times and even requested the calls between me and the agent when I the contract and when I called and cancelled and I have not been called to resolve this matter not been sent to someone who can clarify this **** SHOW for me, as it stands on my credit report it says that I have missed 9 ****ing payments for a ****ing sim card that has been long deactivated. Can someone fix this ****!!!