Billing problems, call limit not working on my line

since november last year i have been complaining to vodacom reagarding my call limit! my subscription is R429p/m and my limit is set at R100 when i used to reach my limit i would phone in and increase it to what i needed. as of november last year that hasnt worked and ive been billed between 800 and 1000 extra on my line every month i phone complain and they pass a small credit as a "good gesture" im tired of complaining and speaking to people in your call center that are very unhelpful... you people are quick to phone for outstanding money but *** useless at sorting peoples complaints out!!! i will not pay you another cent until my problem has been fixed!!!!!!!!