contract cancelation

I have a contract phone with vodacom and i have never missed any payments. The last debit order went off on the 26th of Sept 2017. after that last debt order i phoned and asked for the contract to be cancelled including the airtime and i was told he was cancelled. after that they went on and put airtime in my phone right after i had told them that i do not want to continue with the contract. Then they debited an amount of R208 from my account on the 26th of october 2017 claiming that its for the airtime that they put on my phone after i had clearly stated that i do not want to continue with the contract. Now my problem is that they keep calling me telling me that my account is in arrears because i did a reversal of that R208. Why question is why must i account for something that was not my fault because now they want me to pay R308 and i am being told that this money is accumulative. I am very disappointed in Vodacom because now they do not want to solve their mess. Whoever put airtime in my phone after i had told them not to must be held accountable for this, otherwise i am taking Vodacom to court.