Unhappy vodacom customer

Good day I now am so furious with Vodacom. My last contract with them ended in December 2019. Since then l have been calling their customer care and billing centre to cancel the contract. I paid up my contract and cancelled. Debit order kept passing through. I could phone them nearly every month to cancel the account, am not using their airtime or dat. I dont even use the sim card. The phone is paid up. Today they send me summons that they are going to blacklist me. I have been emailing and no response. I call their call centre you cant get through it requires the old number which when l put there it says number not valid you cant get through. Can someone help me to resolve. I cant believe that Vodacom can have such incompetence as big as they are.