********** Upgrade

After a long struggle about a ********** upgrade on my 3G account, which I have now cancelled ***), this update was one at the end of January 2015.I now get a request that I owe R342.55 that is airtime that was used on that upgrade. How do I pay for airtime that I didn't receive? I have called the call centre and logged a dispute (A1-X3H3-VR814K) for this amount on the 8/05/15 and another one on the 20/05/2015 (A13O9-20Y15Q). Got feedback by sms on the 26/05/2015 that all was rectified and someone called me from ***** from *** at 16:27 to say the same thing. I paid my account as per normal on the 1/06/20015, to my surprise I was to be told I am still owing this amount R342.55. I called again on the 3/06/2015 at the accounts department, they sent me to ***** department and ***** department said they did the investigation and this amount should be cancelled by the accounts/retentions department. Accounts say they cannot cancel the amount it must be done by upgrades. I am passed from one department to the next and I am getting on services for this. What do I need to do to get this amount of R342.55 to be cancelled because I am not liable for it. Account number I***.