Billed for packet switched data with 0 usage limit

When I took out my contract upgrade with MTN I specifically requested that the limit be set to zero and for a few months there were no problems. but for the last few month's I have been billed ridiculous amounts for packet switched data. In June I called call center to complain and they set my lit was set to R300 and I said they should make it zero and they told me they cant. they then gave me instructions to set it to zero but now three months later I'm still being billed crazy amounts I don't know. R506 in june for packet switched data, R333 in july and R340 in august. I buy additional bundles every month and I don't understand whay MTN is charging me these extra costs. the last time I set that limit to zero was there in June when I called and its still zero now but the invoice says something else.<br> <br> This is unacceptable!!!!!!