Vodacom failing to cancel contract phone.

I have two numbers on my Vodacom contract. One number was used by my late husband who passed in April 2010. Since then I have been trying to get the number either cancelled or to change it to a prepaid number. I am not using the number at all, but would have liked to retain the number as a backup. However, in spite of countless calls to get this done, to date I have had no joy from Vodacom. I just calculated that I paid Vodacom in the region of R22,000 for something that I am not using and they are not cancelling. I cannot just not pay, since I am billed for both numbers on the same account, so if I short pay, they suspend the service on both phones. I cannot cancel the primary number as this is an advertised number and I will lose my income if people cannot reach me. Every single time I call in, I get told my account is on the M2-system and someone will call me back within 2 minutes. Hundreds of these promises and to date not a single call-back received. Just this morning I received no less than 4 of these 2 minute promises............