Costly cancelation/incorrect advi*****t

My current contract has come to an end and I have been trying to cancel it since March/April but was advised I can only cancel in June as this is when my contract ends. I was advised to cancel on the earliest date of 6th June, however I was sick and unable to call.

I called in today (2022-06-14), as I am now well again and was told that my bill for next month will now be at a way higher rate due to late cancelation as I could have cancelled from the 11th of May. However, I was never advised that I could cancel from this said date. I was advised the earliest was 6th June. On numerous calls I received from Mtn for upgrades, I did inform them I would like to cancel. The last call I received, I was told I can cancel from the 11th of June.

I am very unhappy with Mtn's cancellation department as their incorrect advi*****t is now costing me more than R700. In an economy that is doing so bad, now I have to find this money for the next bill.