Cancellation of my contract and bad service.

Yesterday I contacted MTN’s retentions department to cancel my contract. I was advised that I needed to pay an amount of R22800,90 by their retentions department which I paid, today I called to cancel my contract and I have been told that I have an outstanding balance of R1193,84. Where does this additional cost come from?? How is it my problem that your staff gave me an incorrect amount to pay.