Brocken promise regarding data cancelation.

Cell C contacted me on the 6th April 2023 to advise that my data contract was about to expire. I then asked them to give me a call the following week which they did on the 11th of May 2023. On the phone I asked them to cancel my contract [as it was about to expire] - I spoke to Catherine. She advised me that my last day for my contract will be the 11th May 2023 and that My last instalment will be the end of May which would be R 384.32 . She further confirmed that there would be no further instalments after May

I received my latest statement on 06/05/2023 via email which reflects that I owe an amount R 979.18 for the month of May. I am not happy about this as I was advised that my last statement and payment would be for May. I phoned Cell C and spoke to Umongameli. He further advised that my last payment and statement would be for 11 days being 1st May to 11 May 2023. I have also been advised that I am liable for a balance owing for the month of June. The annoying part is that they did not communicate with me that cancelling my contract on 11/04/2023 that I would still be paying until June and that the amount I’d have to pay would increase threefold.

I need to get this matter resolved as I have a budget that I need to keep too and cannot afford these additional amounts.

Please advise how the above can be remedied without any additional cost to me.