Charged for acknowledged ********** account

A ********** upgrade was done on my account. The ***** division of Vodacom sent me a letter acknowledging that I did not authorise the upgrade. <br> However, they are now billing me R13 000 for this upgrade, stating their system cannot write off this ********** debt, and I have to pay it, upon which they will then only credit my account and not refund me. <br> I don't have such a huge amount to pay for something I did not buy, which they agree with! I was told that it is not their problem and if I cancel my debit order they will hand me over to their legal department!!! <br> <br> This is proposterous!! I have in my posession their letter absilving me of the upgrade!!!!!