end of contract but i must still pay?

I have a LTE unlimited contract with telkom on the 9th December 2022 the contract ends, I called Telkom on the 16th November 2022 to notify them I will not be proceeding with it, the agent I spoke to told me that the contract will end on the 9th December 2022 and I will only pay for the 9 days Pro Rata, I called Telkom this morning to follow up on it and the agent advised me that I will have to pay December in full and January, I don't understand this as he told me that it will end, why must I pay for something that's ending????