Incorrect overcharge on closed capped data line

Good morning<br> The problem started when I received a bill for 3G data line *** in July 2015 for R12 455.50 . This contract was taken out December 2013 and it is a closed line/capped line on which I contracted for, to only pay R159.00 per month.<br> I have been paying and have been billed correctly for R159.00 for the past 18 months. When I received the huge bill I immediately queried it with numerous calls and e-mails stating the persons I spoke with and the reference numbers and my e-mail dd 28 Sept still they cannot seem to solve it and they keep suspending the services of my other phone *** then I must ohone them just to hear they still dont have answers. My phine got cut off again this morning! I am terrible inconvenienced and sick and tired of talking to call centres!<br> Please help me as their computer generated replies on e-mail is not clarifying the issue nor bringing this to a close or solution.<br> Thank you<br>