Bad service & cant change bank details

I upgraded my contract about 2-3 months ago. I requested for the bank account debit details to be changed, the lady that helped me said I just need to fill out a form so I did. When I arrived home, the lady called me to say she forgot to let me sign some papers for my upgrade. So I said I cannot come back she should email them to me and will sign and send it back. So I did that the lady then said it's not scanned and she cannot accept it. So then when I could go to the store I dropped it off. The lady said finally like it was my fault that the papers were not signed when in fact was her fault and I did her a favour by coming to drop it off. She then said to change bank details she needs bank statement and I'd copy, which she never told me when I upgraded she just said I need to fill the form in. So I then had to run around to get it. I gave it to her the same day. She then called me after a week to say its not allowing her to change banking details. She will send me something else. It's now almost 3 months and still i cannot change my banking details. I have closed that bank account on Saturday as I was paying over R300 to keep it open just for my mtn debit order to go off. So now can someone assist to get my bank account details changed. Really disappointed in the hassles I had since upgrading