Subscriber usage limit

I took out a new contract in January. I specifically asked the salesperson to limit my usage to R0 as I do not want to pay more than the contract amount. He confirmed that I can do that when the contract has been approved. I went back the Sunday to collect my phone when I received a message that the contract has been approved. I requested Tumi, who assisted me, to set the limit to R0.00 - again. She confirmed that it has been done. She gave me a printout of how to set the limits on my phone, but as this was not my phone but rather for an elderly couple, I again asked her to confirm that the limit was set to the contract amount. After receiving the first invoice, I realised that the limit was not set. I phoned account enquiries from my phone, sent e-mails, spoke to Sibusiso (Ref***6 March), Karabo (17 March), Jenpeline (again 17 March) and Zanele (Ref ***, 28 March) - No luck.. All I hear is that I'm liable for the additional monies. Who was liabe for doing their job??? Zanele even promised that her manager would phone me back - he's probably still in a meeting since Monday... Zanele's service was horrible as well - sighed like it was too much effort to help