Easy to apply for a contract but hard to get rid off!!!!

I phoned Vodacom last week to get a settlement on my account as I want to port my number to MTN. I received the early cancellation amount, made payment and received SMS's and emails confirming that my contract was cancelled and moved to prepaid. I received an sms yesterday stating that my port request was declined and after phoning Vodacom was told that there is still an amount outstanding. HOW is that possible when I paid the settlement? I tied multiple ways to contact Vodacom to get the outstanding amount and reference number so that I can pay EVERYTHING but the customer care system is a useless computer system and my multiple emails remain unanswered. How do you get rid of a company that's holding your 20year old cell number hostage?????