my bill is not as per our agreement

Good day I upgraded my cell phone last year August. My contract is supposed to be R100 per month. Since the upgrade I have never paid R100. I cannot send sms. I called the help line and they told me it was sorted but it is still not sorted. I am paying ridiculous amount and I went to the branch and they sent a request to a certain department so that my query can be resolved . Every month I go to the branch and the staff members always go an extra mile to assist me. Still my problem is not solved . This problem is creating a bad record on my name. I am tired of paying all this ridiculous amount.<br> The mtn staff member also send a request for a refund of the amount that I was billed. I received an sms that I must pay 64.04 and when I go to mtn the amount is more than R200. I want my money back, they must sort out the problem and they must unblock my phone<br>