Prepaid Billing sudden jump by R200

I have been with Nashua Mobile then Altech Autopage and never have I received such atrocious service! I have been on a Straight Up 100 TopUp + SIM for years now and since being on this package I have received R100 airtime, 100 smses and 100MB data every month. When all this runs out (moreso the airtime and data) I go online and top myself up with prepaid airtime. I specifically remember asking Altech Autopage to put me on a package that does not gain any extra charges and it seems Glocell failed to pick up on that by suddenly charging me for data and call costs that I paid for with prepaid airtime! Glocell why has my upcoming bill suddenly increased by R200? This is unacceptable service and needs to be rectified.