MTN did not bother to do

A ********** upgrade was done on my name in September 2015. I got an sms to say that my upgrade was sucessful. As I had not signed or asked for any upgrade, I phoned 808 and an operator told me that no upgrade had been done. However, when I received my statement the following month, my normal contract fee of R330 jumped to over R900 because of this. I have had no joy trying to sort this mess out. I have sent numerous mails, to various departments, and every time I have been asked to send an affidavit and certified proof of address which I did countless times. and yet NOTHING was done. After paying by debit order for 25 years, I cancelled my debit order and paid by EFT for the amounts that I WAS responsible for, according to the contract I HAD SIGNED for. I eventually managed to change my account to pre-paid, but I am now stuck with with the ********** outstanding amounts and it is now reflecting on my credit report. This is a fault on MTN's side, yet I am the one that has to sort this mess out. MTN is just not bothered to do anything about it, since September I have had almost no feedback regarding the progress re this matter. Very disappointing and very bad customer service!