Contract wrong and wrongly charged, no fixing acc

New cell phone contract taken in December 2014. January 2015, Bill of R3000 received, hardly ever over R1000 pm. On contacting MTN Kollonade, they show me ,new contract not correctly locked in. Still on old 100mb, and 350 min. New contract is 500mb, 350 any time min. Store clerk send email for MTN to fix mistake. No reply from MTN. I paid R1500 and wait to see what real amount should be, I can't be kept responsible for their mistake. They cut of my phone(business phone) 10 Feb. Kollonade branch manager Belinda Lombard send another email, no reply from MTN.12 Feb I send my own email, 17 Feb I get reply from Eunice Modise, account will be fixed and ref nr:*** is given. 23 February I receive threat letter from MTN , that they are going to suspend my contact and that I must pay back phone. 24 February I send another email, no reply, no account fixed. I phone 24 February 808 and explain that I will have to take legal action against person responsible for my phone being cut of, they reinstate my phone. New bill received, paid in full, still old problem not fixed. 6March another email send, no reply. 9 March they cut my phone off again. Nothing has been done by MTN to fix this