OVER CHARGED!!!!!!

I started a new contract with MTN last year. My contract was for R250.00, i then added the R99 for 500mb which made my contract a total of R349 and i had the agreement to cut off when i had reached my limit. the first couple of months were perfect. January this year i was charged R550.00. February i was charged R600.00. i went into the LaLucia store and was advised that there was a usage limit failure and that this was happening to many people. their system was down so she showed me a list of people that needed to be credited. i was assured that the following month i would not be charged and my account would be credited. March i was once again charged R550.00 so i went back to the La Lucia branch. unable to help me and sent me to the Gateway store who advised that there was no record of anyone ever asking for my account to be credited. i was given a reference number and assured it would be sorted. i went back when i recieved my statement and was told that i wasnt going to be charged and that my account would be sorted to go back to the original contract of R349 per month, i was debited R570 again this month. you are *****ing money and going against the contract that i signed!