DAY LIGHT *******

I am appalled by how MTN has treated me as a customer i have been using them for the past 4 years but cant wait for my last installment for this to end . I upgraded my phone in April on MTN Active specifically asked for a top where i would be paying R500/ month, I got the shock of my life when i got a bill of over R 5000 which i went to a MTN shop in Observatory St Peters Square to complain i was told it was data out of bundle billing usage. The person managed to fix the problem and now i top up when data runs out . The problem is the balance MTN refuses to take responsibility that it was their error and say i need to pay for it .They record all their calls and i have asked them to pull out the conversation i had when i agreed to the contract . I gave them a call today only to be asked how much was i willing to pay and that i will get a bad credit rating cause of this .but my problem is paying for someones mistake that's ******* and they shouldn't be allowed to take advantage of their customers like that.Please may you help me get out of this mess