Cancellation

Good day I'm very unhappy with MTN it's been more than 10months to correct my contract I've signed for. They just add data like they want now I have to pay for there mistakes. Is there another number i can call accept 135 who can assist. Can anyone give me advise and contact details, I send alot of emails. And phone calls. I even have all the references of the calls. But still nothing done. When we call them they put the phone in my ear. Now I have received an SMS to state they will blacklist me. Can anyone assist me in this case