Payments query

I’m not happy as a client for cell c, i have a contract with cell c. This misunderstanding started in May when there was a reversal that happened in my account, I called in to confirm, but i was told everything seems to be fine, in June there was a double debit, but to my surprise the amount was more than what two months is supposed to cover,well I called in and they explained what was tthe reason , I did not mind but was just amazed on the amount, few days ago i got an sms saying my account is in areas, and I called in this morning and I spoke to Thato she told , im being charged a penalty fee, which according to the amount I paid in june it was already included, when I asked her to transfer me to the financial department she told me I need to send proof of payment., my argument is that why do I send something they already have in their system, i need this to be solved immediately as my payment date is in two days.