MTN - Poor Account service

I renewed my contract with MTN. It was for 36 months at a rate of R1069 per month. I am being charged a rate of R1519. I have repeatedly queried this and given case numbers and am informed that this will be escalated and resolved. The consultant verbally confirms that I am being incorrectly billed for a 36 month contract. I only receive case close sms's and the issue does not get resolved and I am stuck paying a high subscription which I had not agreed upon. I sent an email 2 days ago. They advise there response time is 24-48 hours....it has been way over that time and I still receive no response.