unAuthorised billing

just before the end of my two year R99.00/m contract, I noticed I had been debited with R169.00 extra. when i queried this, I was told it was for DATA. I did not request this and was not sold it telephonically, the call centre person assured me it was now cancelled and I would not be billed again. Sept 2015, I was again debited, so I asked the bank to return the debit. on 18th Feb 2016, I received a FINAL DEMAND dated 18th January for an amount of R280.00 I called the Legal department at VODACOM this morning and spoke to a lady whose name sounded like Sibonyela and all she kept saying was 'I MUST UNDERSTAND IT IS FOR USAGE' I told her I did not have the option to run up an account, when the airtime ran out, I 'TOPPED UP' after us repeating ourselves several times, to no avail I told her if it was not rectified I would expose their ****, and put the phone down. how much money do they accumulate from debiting people that have busy accounts and don't notice these 'small amounts' until much later when they get their statements. i would greatly appreciate your assistance.