Want to end contract but quote is ridiculous.

Want to end my contract that I took out from Nashua mobile, and they gave me a verbal amount of R5000 rand a few months back. Now when I want to cancel the contract as it moved over to Vodacom they quote me R18000 for a cancellation. I can not pay that amount as this is the total outstanding for the contract all most. They just give me a answer that it is system generated. I need to end contract as I have been transferred to another Country for work and will not be able to carry on with this contract.<br> <br> Vodacom is crazy to do this.