Telkom is a ****

I had a contract with Telkom which ended on 05/07/25. I called them on the 05/06/25 to cancel the contract as required to do so 30 days prior. I was given a reference number that the contract was cancelled for both lines which were under one contract. In August I receive a bill from Telkom,I dispute the bill as I was told that the contract was terminated,but now they are stating that they only cancelled one number. How is it my problem that they cancelled one number when I clearly stated that I am cancelling both numbers as they contract is due to end in July. They don’t want to take accountability instead they keep saying it was not cancelled even after I provided them with the reference number that I called in and cancelled the contract.