MTN refuses to port my sim to prepaid.

My contract ended with MTN and when I call to port to prepaid they DO NOT answer my call. I held for over an hour until I decided to select the upgrade option and get help from there. They conveniently answered within seconds and when I explain that I actually wanted to port to prepaid they offered to transfer me to the relevant department only for me to hear a recording telling me the number I had dialed is incorrect. I called once more and again selected the upgrade option and again they conveniently answered within seconds and the same thing happened. I find it quite annoying that when you want to upgrade they're so quick to be of your assistance but when you want to cancel your subscription or port to prepaid no one is available to help. I WILL NEVER SUBSCRIBE TO ANYTHING MTN AGAIN!