Why is it impossible to disable voicemail on mtn contract

Why is it so difficult or near impossible to disable voicemail on mtn contract?

The website says, dial *132# and use option 2. However that just says that is only for payasyou go and I must call the callcentre. I call the callcentre, get to a so called chamption, and the champion says to use *132#. After I explain, no this says for payasyougo, they say I must disable this in my phone settings. There is nothing about voicemail in my phone settings, it is carrier side. Then they are so clueless, they want me to go in to a MTN shop. WHY!