Cant understarstand

I have a vodacom 2G data ****le.For the previous 5months I have been billed R129.00 the amount accepted by vodacom for the contract. The end of January I get billed for R2300 what for I would not know as I agreed on a 2G fix monthly data contact. Called numerous times and was told that I have no choice but to pay the whole billed amount, they told me that this was an open line, definitely not something I agreed to.. I emailed a dispute last week Wednesday and still I could not find any help regarding the matter as no one even rep**** to my enquiry.. I feel this is ridiculous. And totally unacceptable.. I have been a loyal customer of vodacom for 6 years and I would not accept