Account Paid but I'm still debited

On the 10th of October I paid R800 into my contract account with Cell C. The plan was that they will debit the monthly R189 from this money for the next 4 months or so. On the 26th of October the money was taken from the R800. Which left R600 in the account. However in November this did not happen, I was billed from my personal account. I logged case with them on the 26 of November to inquire about why I was billed and to find out where my R600 went but I could not get the right answer and a case was logged reference number: ***. 7 days later I still did not have a response from Cell C. I called again to log another case reference number *** and I spoke to a guy named Senzo who told me there was an \adjustment on my account but could not explain what that is to me. How is an adjustment done on my account without my consent. He advised that the case will be attended to in 48 days. Today