my data bundles have been removed from my balance

on the 1st of May 2015 my airtime account was topped up with the normal 1024 MB. On the last day of my contract the 10th May the remaining 600MB disappeared but the airtime and Sms/MMS balance is correct. I have a screen shot to prove this. Nomsa the customer care call centre agent insists that my account was not topped up with the monthly 1GB. My dispute reference number is ***. on dialing the *101# for the nExt debit amount the full debit contract amount is showing. Why is CellC going to debit me for the full amount when I do not get the full package benefits even on the last month of the contract? <br> <br> I'm also not going to run a month on month agreement with CellC anymore as I am incensed by the way I am being treated after being a loyal customer for the last 24 months.