Paying for Data not used and being handed over

Firstly, I have a cell c data contract R149 per month 2G daytime and 3G night time. There are months the data ran out which was accounted for and we did not use. When calling Cell C customer service i get horrible service and attitude and they keep saying we HAVE used the data. Secondly, i am due for an upgrade when phoning i was told i was handed over to pre-legal for missing payments. How can i have missed payments when they debit my account each and every month on the 21st R149.00. I have phoned numerous times but nothing has been resolved as i cannot get through to their pre legal department. I have spoken to a Manager and he has still not returned my call to give me feedback. I have also emailed Cell C and have received no reply. This is unacceptable and a bad record on my name. I would like some feedback urgently please.