Debits incorrectly debited

Beginning of last year I was told my TV licence was in errors, so I told Nu- debt the debt collectors to deduct the entire amount from my account. I had not received email nor post about my account being in errors, so it shocked me and I wanted to settle the amount. I agreed to the full amount being deducted from my account, end of month approached and the full amount was not deducted instead a R17 amount was deducted, the next month a consultant phoned me and again I agreed to the entire amount being deducted and a different amount was deducted, this went on for the remainder of the year, till when I asked an agent to transfer me to a supervisor and I spoke to them and they hung up, I spoke to a different agent the next month and asked for recordings and they advised me that a manager would call me. Up until now my account has never been deducted with the amount I have agreed on and deducting R17 is how much bank charges for me? If you can listen to all the recordings, as proof because I need to take this matter further, to agree on full amount payment and have agents hound me and sms's threatening my credit record when all I have received is poor service from Nu-debt collectors!!