Vodacom are useless

I am moving to the UK for a year, and I have tried to cancel my vodacom uChoose Flexi 200 contract on numerous occasions. However, each time I receive a quote from the cancellations department, the maths does not add up. I am being charged at least R300 extra. I then contact the call centre and they cant help me, they say that it's a computer generated quote and they can't review it. The vodacom stores don't deal with cancellations either. So what am I meant to do now? Vodacom are useless.