Terrible service from MTN

I have been trying to cancel my MTN Data contract for over a week now, I call 135 many times in a day and I hold for at least 2 hours without any response. But when I chose the option to upgrade I immediately get responded to. When I ask the consultants to transfer me to contract cancellation the call will just say "the number you have dialed is not available". I am tired of holding the line only to be cut short by consultants or made to hold forever. I want the contract ASAP as it has expired.