Vodacom

I had a contract with Vodacom for 24 months which ended September 2020. I never missed a payment, my account was always up to date. I have been calling Vodacom since August 2020 to inform them that my contract is ending very soon and I would like them to stop debiting from my account and im not interested in anything else. Nothing was done, the people I spoke with said they are attending my request. I called more than 3 times speaking with different people and they all could not assist me. After the 24 months ended, they debited 3 times from my bank and I was able to reverse the last 2 debits and block them from debiting on my account. They have been sending me messages saying that I owe them, now is R1200. I dont understand how im owing them or why when they are the ones not doing justice to me. I still have the contract I signed and call records. They also record our calls, that can also prove that I called them. How is it that more than 3 people from a large network fail to assist me with one matter, this is not being ***********. I seriously do not know what to make of this. They now even threaten to blacklist me and for what?