Terrible service from Cell C

Terrible service I received from Cell C. I arranged for payment and they decided to debit a portion of amount agreed upon. I called the following day to follow up but they told me the account is up to date. The following month after deducting monthly installment they disconnect the line and tell me I'm in arrears. I didn't budget for that amount cause I thought I was up to date as per the agent. They can't even call to inform me as the customer that I'm behind with payments. I'm looking for a way out