Can't cancel debit order to change to pre-paid.

I am trying to cancel my debit order to go onto pre-paid. They are charging me R185 a month for airtime and 1 gig data. I don't need the data and never ordered it ! Now they're trying to push the airtime. This phone is not used much and that's why it's cheaper for me to go on pre-paid. I'm then told by their consultant that should I cancel the debit order I will lose my number ! This is now the 2nd time I'm trying to cancel the debit order. The first time was a month ago .Vodacom's account's department used to be the best but now the rot is setting in. The number in question is *** .Before the conversation ended the phone was obviously put down by them. Debit orders have become dangerous in this country !