MTN can't to deactivate my number and let me port

I left MTN to Cell C as of teh 1st of September 2015. Today marks the 13th Day where MTN has assure me me they will deactivate my number and have not done so. The whole of last week I went to their morning side customer center and asked them to assist. They kept on saying when you wake up the next day your number would have been deactivated. So now I have to have two cell phones with the same number. One to receive calls from all the other networks and one to receive calls from MTN. Now do you see why I left. They cant get anything right. Why is it so hard to do such a simple thing. All the way from the head of porting to the morning side customer care manager. Here is one of the many reference numbers ***. Just deactivate my number and let me go.