Vodacom cancellation

I have been trying to cancel my son and daughters cell phone contracts as they have immigrated. i have now phoned the cancellation line 4 times with no satisfaction. i either get cut off, they cannot get my details correct, or promise to call me back which they never do. i am quite desperate, what do i do?? I have all the correct details. it seems to me that the staff on the cancellation call centre are not very well trained in this field.