Dispute on settlement of contract

I settled my 2 contracts with Cell C on the 23/10/2015 and I was given the settlement figures by the Branch at the Glen shopping mall. The friendly consultant helped me and I was informed well the amounts paid. the only thing I did not achieve doing was to phone the 084143 number to inform them of my settlement. I paid cell C R2549.33 IN SETTLEMENT. I am really disappointed to know that they are taking this as an upfront payment and not the settlement as intended. They refuse to look into the matter further and hold me responsible for not phoning they 084143 number as was requested. My point is I have called the 084140 number after hours to inform them of my settlement and I certainly do not have time to call during office hours as I do work.<br> I refuse to pay Cell C any further money and I feel that they should have picked up that I paid them such a huge amount other than my instalment and contacted me with this regard. I need this matter resolved without asking me for further payments as I have committed myself with other responsibilities. Please help. unfair service.