********* business practice

I bought Samsung TAB 4 at the Glen MTN branch on the 16th of April 2015, I indicated to the consultant that on the billing option I want the option that automatically cut when the data allocated to get exhausted so that I don't carry the huge bill, but the lady did opposite of my instruction. I used the data under the impression that the Internet will cut once data is finished, that didn't happen until I got an sums saying that my limit is exceeded and that my bill is R1800. The R1800 was deducted end of may, I went to the branch the following day to get explanation, I was told that she was off sick, but her colleagues suspected that she probably forgot to change the system in line with my request.i logged complain with MTN, I haven't received any feedback. Why do I have to pay so much huge bill caused by they incomplete of their staff?I had so much respect for MTN until I became a victim of ********* business practice, I will advice people on my platform against MTN contracts. I won't let this slip without a punch