MTN SIM Contract

I took a Sim Contract with MTN in 2021 , the agent called me , and offered me a contract . The SIM card was delivered to my address. On the call we only agreed on a 24 months contract ending in February 2023 .. I never signed anything and I was never told that i have to send an email for a cancellation a month before the contract ends . A month after i took that contract I wanted to cancel but I was told that there will be a fee that a have to pay for an early cancellation. Then I decided to continue with the contract . Then this year in February the contract ended and I paid the balance I was owing . Then 4 months later I am getting a bill that says I owe R7000 because I didn’t cancel the contract, I don’t know how they got to that amount because I was paying R300 per month.And I was never told that I have to cancel the contract when it ends , I thought they do it automatically or I will get a letter that informs me that I have to cancel it . The sad part about this they stopped that SIM card in February , I never used the data but they expect me to pay for it . If I knew about all of this I would have never took that contact . When I call the customer care to cancel it they are saying I have to pay that R7000 first , which means they continued with the contract without my permission because we only agreed on 24 months . And nothing more .