Change of number issue

I have phoned the call centre on 12 of April 2015 to change my number due to being stalked by a person involved in selling diamonds *******ly and reported it to police and need to change number since the policy is not doing anything to help me, they said theirs problem, due to the number a MTN number where, after week they phoned back and said sorry they got only back to me now, that was week ago, this week I phoned again to ask why it was not yet changed, then i was told it was and deleted number, then they told me Friday that they will follow up within 48hours well that's all most done to and i still receive calls on my old number from the people stalking me!