CONTRACT CHANGED TO PREPAID WITHOUT INFORMING ME!!!

27th August my Vodacom account was not debited as usual and I did not get my 500mb data, so I assumed it's an error they will debit the account and give me my data, comes 27th September still nothing, that's when I called Vodacom on the 12th October seeing now its 2 months and I know for a fact that my contract with them only ends in April 2018. When I called I was told that my contract sim has be converted to pre-paid on the 8th September because they suspected ********** connection and I owe them R 2 557.01. After I called them a complaint was logged as my question was "why was I not told??" how do you changed my contract to pre-paid without telling me???? I had to wait for 14 working days for them to come back to me and still no one cared to come back to me I called back myself after the 14 days had passed and I was told that this matter is now referred to subscribers activations but only if I pay that amount they can open my sim back to contract...still I had to call to hear all that information!!! Now I do not want anything to do with Vodacom anymore, I have been inconvenienced for 2 months without data, since they took it upon themselves to convert the sim without my knowledge they must write off that amount without my knowledge as well because I will not pay it!!!