How do you get rid of Voicemail?

I have been trying for about 2 and a half years to get the voicemail function on my account cancelled or at least converted to voicemail lite, but no luck/service. I have tried in-store when upgrading and at the customer service number (various times) as well as the USSD code (old and new).

The agents keep telling me I am not registered for the service, but why do I keep on getting the SMS's that informs me that there was a voice message left for me? How can I not be registered? I really cannot recommend MTN to anyone.