The business number you have dialled, does NOT EXIST

I have been trying for MONTHS to cancel the voicemail on 2 business contracts. After numerous calls and emails, the voicemail was eventually cancelled - TO MY FRUSTRATION Whenever a call is not answered, the caller hears - "The number you have dialled, does not exist"

Really MTN???? We made numerous attempt to fix this, but we only get more frustrated with unanswered e-mails, hours waiting times on call centre lines and zero solutions.