Outrageously high phone accounts

My partner is with Vodacom and has received two outrageously high bills in the past two months, apparently for high data usage?? Going back into history the monthly bill never exceeded a certain amount. Since upgrading her phone and package a few months ago the bills have increased immensely. Last month a consultant was still looking into it but insisted that the amount had to be paid first. To date no feed-back. Today another even higher bill shocker again. Complained via phone, awaiting a supervisor's call back and C has just sent a nice long e-mail to their CEO, Mohamed Shameel Aziz Joosub. I believe there have been many similar incidents experienced by other Vodacom users? Is the only way forward to take legal action??