Paying fir something not advised of

I had a contract with Vodacom and cancelled my contract in June and the next day I was on prepaid. Very impressed with the service, THEN, not anymore... All of a sudden July, my account is debited with a Vodacom debit order.

When I phone in I am told that I need to pay that and I was supposed to be advised when my settlement quotation was sent.

I phoned in more than 2 times and not once was I advised I will still pay a bill for July. (Which I forfeited the benefits when I cancelled). I reversed my debit and refuse to pay. Again debited in August with a higher value. Again. I will not pay for something I was not advised of....

Not even in the quotation sent to me was I advised,,,,

I kniw that this amount can be written off. Do not tell me I owe something that was cancelled.

Your urgent response will be much appreciated.