MTN ******** customers out of money

I took out a contract somewhere at the beginning of 2017 and i explicitly to the guy helping me setup the contract that i did not want to be able to go over my contracts limit. so when my 2Gb of data was finished, i cut me off and i could top up when i was ready. several months down the line after having had a consistent bill for the past 10 or so months, i recieve a bill for R500 more then normal. it must have been a mistake so i call them the following day and discover that mtn had taken it upon themselves to change my limit to R500 over. me, none the wiser of the change, used my data as normal and managed to easily and unknowingly hit that R500 mark. they excuse i received was "no, you got an sms about your limit increasing " so i went back to find it. finally after searching for a while i found the sms which i had passed off as a promotion after a quick glance. MTN had the audacity to change my limit without my permission or consent and according to the sms, i had to act to stop the change... now i'm down R500 just before christmas time...