Bad service

I went to MTN to upgrade my phone contract to a sim-only contract for R99 pm for 12 GB , firstly I still haven`t received my 12 GB . Also I was led on by the sales lady that my debiet order will only be R279 for this month but my debiet order was R569 which was my old contract payment and this was returned by ABSA because I only left enough money for my new payment which was R279 and not R569 and when I called them after many attempts they only inform me today that if you upgarde after the 11th your payment will still go of on your pervious accounts payment and not your new payment, which nobody told or informed me about now I have to pay the R569 and also a huge amount of returning fee to absa and still I have not received my 12 GB . I am very very very angry !!! And still nobody called be back , I want the fee`s of the returning fond on my bank account to be paid , I want my data as well or I will stop my account with MTN !!!