Why do I have to pay for your system error VODACOM?

I tried cancelling a contract in November and I was advised even though the Upgrade is due the contract can only be cancelled end February 2023 so I must call end January to cancel the contract. I called end January from *** to cancel the contract of *** and I was assured that the contract will be cancelled end February 2023. Last payment for both numbers will be end February. My daughter who is using the phone then advised me today that airtime was loaded on the number. She was already treating the number as pay as you go so she doesn't need the airtime. Thank you Vodacom. I called and spoke to a lady by the name of Zama at 10.45am on the 4th of March. She sees I cancelled but due to a system error the cancellation never went through but she will put it through for the end of March and she sent me a SMS confirming this. Why do I as the customer have to pay for your system error thanks to my daughter informing me of the fact. Who was going to pick up the fact that the contract had to be cancelled? Why am I paying the price? Please rectify your system error and cancel the Contract as at the end of February as per the arrangement. I am sick and tired of paying for the big companies System errors. It is just not fair Vodacom